fileset: actually implement 'minusset'

  $ hg debugfileset 'a* - a1'

was tracing back because 'minus' symbol was not supported.

mercurial/fileset.py

@@ -107,6 +107,11 b' def notset(mctx, x):'
     s = set(getset(mctx, x))
     return [r for r in mctx.subset if r not in s]
 
+def minusset(mctx, x, y):
+    xl = getset(mctx, x)
+    yl = set(getset(mctx, y))
+    return [f for f in xl if f not in yl]
+
 def listset(mctx, a, b):
     raise error.ParseError(_("can't use a list in this context"))
 
@@ -406,6 +411,7 b' methods = {'
     'symbol': stringset,
     'and': andset,
     'or': orset,
+    'minus': minusset,
     'list': listset,
     'group': getset,
     'not': notset,

tests/test-fileset.t

@@ -36,4 +36,6 b' Test operators and basic patterns'
   b1
   $ fileset '! ("a*")'
   b1
+  $ fileset 'a* - a1'
+  a2