fix parsing of tags. make parse errors useful. add new tag tests. old code read every head of .hgtags. delete and recreate of .hgtags gave new head, but if error in deleted rev, .hgtags had error messages every time it was parsed. this was very hard to fix, because deleted revs hard to get back and update, needed merges too. new code reads .hgtags on every head. advantage is if parse error happens with new code, is possible to fix them by editing .hgtags on a head and committing. NOTE: new code uses binary search of manifest of each head to be fast, but still much slower than old code. best thing would be to have delete record stored in filelog so we never touch manifest. could find live heads directly from filelog. this is more work than i want now. new tests check for parse of tags on different heads, and inaccessible heads created by delete and recreate of .hgtags.

changeset:   0:0acdaf898367
tag:         tip
user:        test
date:        Mon Jan 12 13:46:40 1970 +0000
summary:     test

b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3 644 a
a
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
1 files, 1 changesets, 1 total revisions