Allow package scoped functions to be called without arguments

The parser currently only allows package scoped functions to be called if
there is at least one argument. But package scoped functions are the same
as normal functions and it is allowed to call them with no arguments. It is
even possible to pass no value for a positional argument, if the positional
argument has a default value.

Update the parser to handle this.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

parse.y

@@ -3723,7 +3723,7 @@ expr_primary
 	delete $3;
 	$$ = tmp;
       }
-  | PACKAGE_IDENTIFIER K_SCOPE_RES IDENTIFIER '(' expression_list_proper ')'
+  | PACKAGE_IDENTIFIER K_SCOPE_RES IDENTIFIER '(' expression_list_with_nuls ')'
       { perm_string use_name = lex_strings.make($3);
 	PECallFunction*tmp = new PECallFunction($1, use_name, *$5);
 	FILE_NAME(tmp, @3);