convert: quote "^" to avoid windows using it as an escape char.

hgext/convert/git.py

@@ -134,7 +134,7 b' class convert_git(converter_source):'
                 changes.append(f)
             fh.close()
         else:
-            fh = self.gitcmd("git-diff-tree --name-only --root -r %s %s^%s --"
+            fh = self.gitcmd('git-diff-tree --name-only --root -r %s "%s^%s" --'
                              % (version, version, i+1))
             changes = [f.rstrip('\n') for f in fh]
             fh.close()