Squashed commit of the following:

Squashed commit of the following:

commit a7e771a2fafea7cb9d184b9ab08d0d436de91819
Author: russ <rucombs@cisco.com>
Date:   Tue Apr 16 09:27:28 2019 -0400

    build: fix lua_plugffi.h make error

commit 561738d9ffc7b6491b618187affe51b379389681
Author: russ <rucombs@cisco.com>
Date:   Mon Apr 15 10:02:53 2019 -0400

    Lua: remove dependency on SNORT_LUA_PATH

commit 6e0cb4c41a389ef6f084ef82c0155acc888f1786
Author: russ <rucombs@cisco.com>
Date:   Wed Apr 10 15:54:43 2019 -0400

    parser: update include file handling

    Unify Lua and rule include handling of relative paths to search in this order:
    relative to working directory, relative to the including file, and if that
    fails relative to the -c conf.  The precedence allows overrides and supports
    processing non-local configurations.