add get_git_svn_revision and fall back to it

Now gramps developers using git need not be ashamed of their
``gramps --version'' output :)

svn: r23118

gramps/gen/svn_revision.py

@@ -22,6 +22,7 @@
 
 import sys
 import subprocess
+import re
 
 if sys.version_info[0] < 3:
     cuni = unicode
@@ -30,21 +31,32 @@ else:
         return s.decode("utf-8", errors = 'replace')
     cuni = to_utf8
 
-def get_svn_revision(path=""):
+def _get_svn_revision(path, command, stdout_to_rev):
     stdout = ""
     try:
-        p = subprocess.Popen("svnversion -n \"%s\"" % path, shell=True, 
-                             stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+        p = subprocess.Popen(
+                "{} \"{}\"".format(command, path),
+                shell=True, 
+                stdout=subprocess.PIPE, stderr=subprocess.PIPE)
         (stdout, stderr) = p.communicate()
     except:
         return "" # subprocess failed
     # subprocess worked
     if stdout and len(stdout) > 0: # has output
         stdout = cuni(stdout) # get a proper string
-        if stdout[0].isdigit():
-            return "-r" + stdout
-        else:
-            return ""
+        rev = stdout_to_rev(stdout)
+        return "-r" + rev if rev else ""
     else: # no output from svnversion
         return ""
 
+def get_svn_revision(path=""):
+    return _get_svn_revision(path, "svnversion -n",
+            lambda stdout: stdout if stdout[0].isdigit() else ""
+            ) or get_git_svn_revision(path)
+
+def get_git_svn_revision(path=""):
+    def stdout_to_rev(stdout):
+        m = re.search("Revision:\s+(\d+)", stdout, re.MULTILINE)
+        return m.group(1) if m else ""
+
+    return _get_svn_revision(path, "git svn info", stdout_to_rev)