minifileset: note the unsupported file pattern when raising a parse error

This was useful in debugging, because I stupidly quoted it out of habit from the
command line.  This isn't a great example that clearly shows the problem, but I
don't know how to improve it.  The problem *is* obvious once a complex statement
or a clearly bogus string is used.

mercurial/minifileset.py

@@ -30,7 +30,7 b' def _compile(tree):'
             pl = len(p)
             f = lambda n, s: n.startswith(p) and (len(n) == pl or n[pl] == '/')
             return f
-        raise error.ParseError(_("unsupported file pattern"),
+        raise error.ParseError(_("unsupported file pattern: %s") % name,
                                hint=_('paths must be prefixed with "path:"'))
     elif op == 'or':
         func1 = _compile(tree[1])

tests/test-lfs.t

@@ -18,6 +18,10 b''
 # Commit small file
   $ echo s > smallfile
   $ echo '**.py = LF' > .hgeol
+  $ hg --config lfs.track='"size(\">1000B\")"' commit -Aqm "add small file"
+  hg: parse error: unsupported file pattern: size(">1000B")
+  (paths must be prefixed with "path:")
+  [255]
   $ hg --config lfs.track='size(">1000B")' commit -Aqm "add small file"
 
 # Commit large file