setup: try parsing /etc/lsb-release first, then invoking lsb_release, because the latter takes half-a-second on my workstation, which is too long

Also because in some cases the former will work and the latter won't.
This patch also tightens the regexes so it won't match random junk.

src/allmydata/__init__.py

@@ -22,16 +22,27 @@ import _auto_deps
 _auto_deps.require_auto_deps()
 
 import platform, re, subprocess
-_distributor_id_cmdline_re = re.compile("(?:Distributor ID)?:?\s*(.*)", re.I)
-_release_cmdline_re = re.compile("(?:Release)?:?\s*(.*)", re.I)
+_distributor_id_cmdline_re = re.compile("(?:Distributor ID:)\s*(.*)", re.I)
+_release_cmdline_re = re.compile("(?:Release:)\s*(.*)", re.I)
 
-_distributor_id_file_re = re.compile("(?:DISTRIB_ID.*=)?\s*(.*)", re.I)
-_release_file_re = re.compile("(?:DISTRIB_RELEASE.*=)?\s*(.*)", re.I)
+_distributor_id_file_re = re.compile("(?:DISTRIB_ID\s*=)\s*(.*)", re.I)
+_release_file_re = re.compile("(?:DISTRIB_RELEASE\s*=)\s*(.*)", re.I)
 
 def get_linux_distro():
     """ Tries to determine the name of the Linux OS distribution name.
 
-    The function tries to execute "lsb_release", as standardized in 2001:
+    First, try to parse a file named "/etc/lsb-release".  If it exists, and
+    contains the "DISTRIB_ID=" line and the "DISTRIB_RELEASE=" line, then return
+    the strings parsed from that file.  The reason we try this first is because
+    it is faster than the official method of invoking "lsb_release" (which takes
+    half a second on my high-performance Athlon64 Ubuntu workstation).  Also
+    because some distributions (at least Debian/Ubuntu) have /etc/lsb-release in
+    the "base-files" package (Priority: required) but /usr/bin/lsb_release in
+    the "lsb-release" package (Priority: important), so it is possible that
+    /etc/lsb-release is there even if /usr/bin/lsb_release isn't.
+
+    If parsing /etc/lsb-release doesn't work, then try to execute "lsb_release",
+    as standardized in 2001:
 
     http://refspecs.freestandards.org/LSB_1.0.0/gLSB/lsbrelease.html
 
@@ -42,15 +53,7 @@ def get_linux_distro():
     If executing "lsb_release" raises no exception, and returns exit code 0, and
     both the "distributor id" and "release" results are non-empty after being
     stripped of whitespace, then return a two-tuple containing the information
-    that lsb_release emitted, as strings.  Why do we execute lsb_release as our
-    first strategy?  Because it is the standard.
-
-    If executing "lsb_release" doesn't work, then try to parse a file named
-    /etc/lsb-release to get the same information.  Why do that?  Because some
-    distributions (at least Debian/Ubuntu) have /etc/lsb-release in the
-    "base-files" package (Priority: required) but /usr/bin/lsb_release in the
-    "lsb-release" package (Priority: important), so it is possible that
-    /etc/lsb-release is there even if /usr/bin/lsb_release isn't.
+    that lsb_release emitted, as strings.
 
     If that doesn't work, then invoke platform.dist() and return the first two
     elements of the tuple returned by that function.
@@ -66,25 +69,6 @@ def get_linux_distro():
     """
     _distname = None
     _version = None
-    try:
-        p = subprocess.Popen(["lsb_release", "--id"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-        rc = p.wait()
-        if rc == 0:
-            m = _distributor_id_cmdline_re.search(p.stdout.read())
-            if m:
-                _distname = m.group(1).strip()
-
-        p = subprocess.Popen(["lsb_release", "--release"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-        rc = p.wait()
-        if rc == 0:
-            m = _release_cmdline_re.search(p.stdout.read())
-            if m:
-                _version = m.group(1).strip()
-    except EnvironmentError:
-        pass
-
-    if _distname and _version:
-        return (_distname, _version)
 
     try:
         etclsbrel = open("/etc/lsb-release", "rU")
@@ -92,14 +76,34 @@ def get_linux_distro():
             m = _distributor_id_file_re.search(line)
             if m:
                 _distname = m.group(1).strip()
+                if _distname and _version:
+                    return (_distname, _version)
             m = _release_file_re.search(line)
             if m:
                 _version = m.group(1).strip()
+                if _distname and _version:
+                    return (_distname, _version)
     except EnvironmentError:
             pass
 
-    if _distname and _version:
-        return (_distname, _version)
+    try:
+        p = subprocess.Popen(["lsb_release", "--all"], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        rc = p.wait()
+        if rc == 0:
+            for line in p.stdout.readlines():
+                m = _distributor_id_cmdline_re.search(line)
+                if m:
+                    _distname = m.group(1).strip()
+                    if _distname and _version:
+                        return (_distname, _version)
+
+                m = _release_cmdline_re.search(p.stdout.read())
+                if m:
+                    _version = m.group(1).strip()
+                    if _distname and _version:
+                        return (_distname, _version)
+    except EnvironmentError:
+        pass
 
     return platform.dist()[:2]