1) Remove lang/gnat-aux dependency
2) USE_LANGUAGES+= ada (invokes lang/gcc-aux dependency)
3) Improve shared library rpath definition required when built by compiler
not installed at ${LOCALBASE}
4) Restore use of pkgsrc wrappers
Removing DESTDIR from the shared library rpaths required a change in the
compiler. To tell GNAT not to add in DESTDIR rpaths, the -R switch
needs to be added to each library's option set. GNAT-AUX 20110627nb2
required at a minimum to take advantage of these switches.
Additionally, issues with installed files' permissions were fixed.
