revset: added lazyset implementation to matching revset

Performance Benchmarking:

$ time hg log -qr "first(matching(0))"
0:9117c6561b0b

real  0m2.213s
user  0m2.149s
sys 0m0.055s

$ time ./hg log -qr "first(matching(0))"
0:9117c6561b0b

real  0m0.177s
user  0m0.137s
sys 0m0.038s

mercurial/revset.py

@@ -1365,18 +1365,18 b' def matching(repo, subset, x):'
     # is only one field to match)
     getinfo = lambda r: [f(r) for f in getfieldfuncs]
 
-    matches = set()
+    def matches(x):
     for rev in revs:
         target = getinfo(rev)
-        for r in subset:
             match = True
             for n, f in enumerate(getfieldfuncs):
-                if target[n] != f(r):
+                if target[n] != f(x):
                     match = False
-                    break
             if match:
-                matches.add(r)
-    return baseset([r for r in subset if r in matches])
+                return True
+        return False
+
+    return lazyset(subset, matches)
 
 def reverse(repo, subset, x):
     """``reverse(set)``