libltdl obscures error messages

[Marius Vollmer]

Hi,

I would like to see the error reporting of libltdl be improved.
Currently, it often happens that a dlopen attempt fails with "file not
found" although in reality there was some other cause for the failure.

This happens because find_file simply tries the next filename
candidate from its search-path when tryall_dlopen fails.  It should
only continue looking for other candidates when the dlopen failed
because of a non-existing file.  All other errors should be reported
immediately and the searching be abandoned.

The same problem occurs when lt_dlopenext tries several extensions.
This function either succeeds, or fails with a "file not found" error.
A intermediate "symbol not found" error, say, is swallowed.

The fix would be to distinguish between "file not found" errors (which
can be repaired by trying the next candidate), and other errors (which
should be immediately passed to the caller).

I don't have a patch handy since I didn't found my way into the logic
of ltdl.c yet.  If you agree that something should be done about this
situation, I'd be glad to try harder.