Copy the Unix environment to the Win32 environment in the unix-adapter.

This should fix issue 5.

The copying appeared to be necessary only for Cygwin, not for MSYS.  I'm
not sure why this is.  I added a call to cygwin_internal(CW_SYNC_WINENV)
for both anyway, because I didn't think it would hurt.

Add a distclean target that removes the files configure creates.