Autodoc should complain when methods are declared in foreign modules.

Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=1901

Reported by Martin Nilsson, IDA nilsson@pike.ida.liu.se

The following comment in builtin.c, generated from builtin.cmod

/*! @decl string String.trim_whites (string s) *! *! Trim leading and trailing spaces and tabs from the string @[s]. */

gets extracted to

Trim leading and trailing white spaces characters (space, tab, newline and carriage return) from the string s.

which is clearly wrong.