[PATCH 2 of 6 sethelp v2] fileset: use UnknownIdentifier where appropriate

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1422300708 18000
#      Mon Jan 26 14:31:48 2015 -0500
# Node ID 0c7f94a49b2fd024e54524f12a02b9b59feb304e
# Parent  4bfb330ca07cdf5eb79c884007b3bfabe69a70bc
fileset: use UnknownIdentifier where appropriate

diff --git a/mercurial/fileset.py b/mercurial/fileset.py
--- a/mercurial/fileset.py
+++ b/mercurial/fileset.py
@@ -186,7 +186,7 @@ def clean(mctx, x):
 def func(mctx, a, b):
     if a[0] == 'symbol' and a[1] in symbols:
         return symbols[a[1]](mctx, b)
-    raise error.ParseError(_("not a function: %s") % a[1])
+    raise error.UnknownIdentifier(a[1], symbols.keys())
 
 def getlist(x):
     if not x: