Make it so out-of-tree builds (autofoo and cmake) have access to the various

Make it so out-of-tree builds (autofoo and cmake) have access to the various
data files (diameter/*, COPYING, manuf) when running *shark from the
build directory.

Do this by passing in the top-level source directory as a compile-time
definition (unfortunately this has to be in the top-level Makefile too because
some programs link directly with epan/filesystem.c).

The plugins dir is no longer below the datafile directory but rather the
progfile directory (if we have one).  Handle the special case of AUTHORS-SHORT
(a data file but a generated one) by checking the file name before building
the path.

https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=5664

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@52940 f5534014-38df-0310-8fa8-9805f1628bb7