Name function in error from canonicalize_macaddress().

In one error raised by canonicalize_macaddress(), the message did not
specify which function was complaining.  Add that to the message.

lib/puppet/parser/functions/canonicalize_macaddress.rb

@@ -66,7 +66,8 @@ module Puppet::Parser::Functions
                 # Two groups of six digits each; "-" or "." as separator
                 canon = groups.join("").gsub(/(..)/, '\1:').chomp(":")
             else
-                raise(Puppet::ParseError, "Badly formed MAC address `#{mac}'")
+                raise(Puppet::ParseError,
+		      "canonicalize_macaddress(): Badly formed MAC address `#{mac}'")
             end
             canon_macs << canon.downcase
         end