Make Lua taps work in out-of-source-tree builds.

make-taps.pl needs to know where to find the source files in order to build
the taps.

This makes the wslua test suite run in autofoo out-of-source-tree builds too.
To make it work with cmake builds requires putting all the epan/wslua/ output
(or at least init.lua) in epan/wslua/ instead of epan/.

Change-Id: I1b3c517f08d3c752ee03cb89482ee4951ceb5bf3
Reviewed-on: https://code.wireshark.org/review/3348
Petri-Dish: Evan Huus <eapache@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Evan Huus <eapache@gmail.com>