make tox env for code-checks

This executes: check-debugging, check-interfaces, check-miscaptures,
find-trailing-spaces, check-umids, pyflakes.

Other changes:

* fix check-umids.py to take starting points. run it as `check-umids.py
  src` instead of `check-umids.py src/allmydata/*.py`
* check-debugging: rewrite in python to run from tox: tox doesn't like
  to run shell scripts.
* put check-interfaces.py last: it produces lots of warnings, but passes
  anyways. The others only produce significant output if they fail.

misc/coding_tools/check-debugging.py

@@ -0,0 +1,22 @@
+#! /usr/bin/python
+
+# ./check-debugging.py src
+
+import sys, re, os
+
+ok = True
+umids = {}
+
+for starting_point in sys.argv[1:]:
+    for root, dirs, files in os.walk(starting_point):
+        for fn in [f for f in files if f.endswith(".py")]:
+            fn = os.path.join(root, fn)
+            for lineno,line in enumerate(open(fn, "r").readlines()):
+                lineno = lineno+1
+                mo = re.search(r"\.setDebugging\(True\)", line)
+                if mo:
+                   print "Do not use defer.setDebugging(True) in production"
+                   print "First used here: %s:%d" % (fn, lineno)
+                   sys.exit(1)
+print "No cases of defer.setDebugging(True) were found, good!"
+sys.exit(0)