manifest: speed up matches for large sets of files

If the number of files being matched is large, the bisection overhead
can dominate, which caused a performance regression for revert --all
and histedit. This introduces a (fairly arbitrary) cross-over from
using bisections to bulk search.

mercurial/manifest.py

@@ -164,7 +164,7 b' class manifestdict(object):'
             return self.copy()
 
         files = match.files()
-        if (match.matchfn == match.exact or
+        if ((match.matchfn == match.exact and len(files) < 100) or
             (not match.anypats() and util.all(fn in self for fn in files))):
             return self.intersectfiles(files)