[configure] Use hg, instead of svn, to compute the version string

Now we moved from Subversion to Mercurial, use the hg command to
compute the version string.

Manually backported from 1409:7264ce426be4 plus 1430:933eee133cbf
as too much changes have been made to ./configure in the meantime.

.version

@@ -1 +1 @@
-1.4.1+svn
+1.4.1+hg

configure

@@ -340,21 +340,13 @@ IFS="${save_IFS}"
 # If we can't get the revision number, use date
 printf "Computing version string... "
 case "${VERSION}" in
-    *+svn|svn)
-        REVISION="$( LC_ALL=C svnversion )"
+    *+hg|hg)
+        REVISION="$( hg id -n 2>/dev/null )"
         case "${REVISION}" in
-            exported)
+            "")
                 VERSION="${VERSION}_unknown@$( date +%Y%m%d.%H%M%S )";;
             *)
-                URL="$( LC_ALL=C svn info 2>/dev/null   \
-                                 |egrep 'URL: '         \
-                                 |cut -d ' ' -f 2-      \
-                      )"
-                ROOT="$( LC_ALL=C svn info 2>/dev/null      \
-                         |"${grep}" '^Repository Root: '    \
-                         |cut -d ' ' -f 3-                  \
-                       )"
-                VERSION="${VERSION}${URL#${ROOT}}@${REVISION}"
+                VERSION="${VERSION}_$( hg id -b )@${REVISION%%+}_$( hg id -i )"
                 ;;
         esac
         # Arrange to have no / in the directory name, no need to create an