Expand environment variables in include files

[mchamberland]

Expanding environment variables in various egs++ applications has been added a while ago, but what about for include file keys in egsinp files? It does not seem to be supported (as far as I can tell...) and looking at the source in egs_input.cpp, I have no idea where the call to egsExpandPath() should be placed.

Can someone add support for this, please?