* libltdl/ltdl.c (sys_wll_open): libltdl expects this function to

* libltdl/ltdl.c (sys_wll_open): libltdl expects this function to
fail if it is unable to physically load the library.  Sadly,
LoadLibrary will search the loaded libraries for a match and
return one of them if the path search load fails.  Simulate a
failure in this case for compatibility with the other APIs.
Also, LoadLibrary takes the liberty of adding `.dll' to library
names passed without an extension, we now add a trailing `.' to
prevent this from happening.