Handle __PACKAGE__ as object name correctly

__PACKAGE__ cannot appear as the object name for indirect calls, but it
can for direct ones. This could cause wrong reports of indirect calls
when the actual package name appeared later in the source, for instance
in a comment. This is fixed by looking for '__PACKAGE__' in the source
buffer when we already have a hit for the current package name, and by
keeping the first one of those two.

This fixes RT #88428.