match: add basic wrapper for boolean function
This serves as a generic wrapper for fileset predicates. In future patches,
a fileset expression will be mapped to a tree of matchers for a better support
of match attributes such as visitdir(). For example,
$ hg debugwalk -v 'set:contrib/** and binary()'
* matcher:
<intersectionmatcher
m1=<patternmatcher patterns='(?:contrib/.*$)'>,
m2=<predicatematcher pred=binary>>
...
https://bz.mercurial-scm.org/619
$ hg init
$ echo a > a
$ hg ci -Ama
adding a
$ echo b > b
$ hg branch b
marked working directory as branch b
(branches are permanent and global, did you want a bookmark?)
$ hg ci -Amb
adding b
$ hg co -C 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Fast-forward:
$ hg merge b
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -Ammerge
Bogus fast-forward should fail:
$ hg merge b
abort: merging with a working directory ancestor has no effect
[255]
Even with strange revset (issue4465)
$ hg merge ::.
abort: merging with a working directory ancestor has no effect
[255]