[Rivet] agile, libHepMCfio and macos

[Dmitri Konstantinov]

Hi Andy, hi all,

There is a problem with running agile on macos. Probably you are aware 
of it.
agile can't find HepMC library libHepMCfio. By default it looks for 
libHepMCfio in system folders:

("/usr/lib", "/usr/lib64", "/usr/lib32", "/usr/local/lib", 
"/usr/local/lib64", "/usr/local/lib32") plus generators directories plus 
directories from LD_LIBRARY_PATH but not from DYLD_LIBRARY_PATH.

Therefore as workaround we can specify LD_LIBRARY_PATH for macos or 
introduce a simple patch src/Core/Loader.cc adding paths from 
DYLD_LIBRARY_PATH to "search" dirs:

To:
        const char* envld = getenv("LD_LIBRARY_PATH");
         if (envld) dirs += split(envld);

we can add:

       const char* envdyld = getenv("DYLD_LIBRARY_PATH");
         if (envdyld) dirs += split(dyenvld);


Cheers,
       Dima