tags: return empty list of heads for no .hgtags case
The caller only uses the heads to resolve tags from content of .hgtags.
Returning a non-empty array is pointless if there is no .hgtags file.
--- a/mercurial/tags.py Thu Apr 16 12:01:00 2015 -0400
+++ b/mercurial/tags.py Thu Apr 16 11:32:46 2015 -0400
@@ -326,7 +326,7 @@
if not len(repo.file('.hgtags')):
# No tags have ever been committed, so we can avoid a
# potentially expensive search.
- return (repoheads, {}, valid, None, True)
+ return ([], {}, valid, None, True)
starttime = time.time()