revset: add partial support for ancestor(wdir())

It's easy, so let's make it happen. I'm not certain if 'wdir() &' should
be required. ancestors(wdir()) works without it, but ancestor(wdir()) doesn't
as of now. That's the issue of fullreposet.__contains__() vs __and__().

mercurial/revset.py

@@ -319,8 +319,9 b' def ancestor(repo, subset, x):'
     for r in reviter:
         anc = anc.ancestor(repo[r])
 
-    if anc.rev() in subset:
-        return baseset([anc.rev()])
+    r = scmutil.intrev(anc)
+    if r in subset:
+        return baseset([r])
     return baseset()
 
 def _ancestors(repo, subset, x, followfirst=False, startdepth=None,

tests/test-revset.t

@@ -1813,6 +1813,16 b' Test working-directory revision'
   6
   7
   2147483647
+  $ hg debugrevspec '0:wdir() & ancestor(wdir())'
+  2147483647
+  $ hg debugrevspec '0:wdir() & ancestor(.:wdir())'
+  4
+  $ hg debugrevspec '0:wdir() & ancestor(wdir(), wdir())'
+  2147483647
+  $ hg debugrevspec '0:wdir() & ancestor(wdir(), tip)'
+  4
+  $ hg debugrevspec 'null:wdir() & ancestor(wdir(), null)'
+  -1
   $ hg debugrevspec 'wdir()~0'
   2147483647
   $ hg debugrevspec 'p1(wdir())'