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.

%%% should show a removed and b added
A b
R a
reverting...
undeleting a
forgetting b
%%% should show b unknown and a back to normal
? b
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
merging a
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
%%% should show foo-b
foo-b
%%% should show a removed and b added
A b
R a
%%% revert should fail
abort: working dir has two parents; you must specify the revision to revert to
%%% revert should be ok now
undeleting a
forgetting b
%%% should show b unknown and a marked modified (merged)
? b
%%% should show foo-b
foo-b