Fix rb_define_class_under parsing

The first argument is an identifier so we need to skip over it.

Really fixes #327

Author: drbrain

lib/rdoc/parser/c.rb

@@ -749,7 +749,7 @@ def find_class_comment class_name, class_mod
                          ([\w\.\s]+\s* = \s+)?rb_define_(class|module)[\t (]*?"(#{class_name})"%xm then
       comment = $1
     elsif @content =~ %r%((?>/\*.*?\*/\s+))
-                         ([\w\. \t]+ = \s+)?rb_define_(class|module)_under[\t (]*?"(#{class_name.split('::').last})"%xm then
+                         ([\w\. \t]+ = \s+)?rb_define_(class|module)_under[\t\w, (]*?"(#{class_name.split('::').last})"%xm then
       comment = $1
     else
       comment = ''