Add branchtags function with cache
- cache stores tipmost node and rev and node,label pairs
- if cache is out of date, scan new changesets
- write new cache out after scan
--
A dir/b.o
? a.c
? a.o
? dir/c.o
? syntax
--
abort: .hgignore: invalid pattern (relre): *.o
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
.hgignore: ignoring invalid syntax 'invalid'
A dir/b.o
? .hgignore
? a.c
? a.o
? dir/c.o
? syntax
--
A dir/b.o
? .hgignore
? a.c
? syntax
--
A dir/b.o
? .hgignore
? a.c
? a.o
? dir/c.o
--
A dir/b.o
--
A b.o