add legacy subdir for mods with 5.1 edition of mod_lua, change languages/mod_lua to legacy/languages/mod_lua in modules.conf to use older lua mod

This is intended to make it easier to describe to users on JIRA how
they should test build patches in a standardized manner and how to
collect a full build log that includes the exact git commit they are
building.

Previously we were including the output of `apr-1-config/apu-1-config
--libs` into CORE_LIBS.  This seemed sensible as CORE_LIBS is added in
the right places to various _LDADD and _LIBADD variables.  However we
also use the value of CORE_LIBS as dependencies in the makefile.
Astonishingly this doesn't seem to cause any issues on most
platforms (or we would have noticed sooner), but it does break things
on Mac.

Thanks-to: Seven Du <dujinfang@gmail.com>

FS-5956 --resolve

There are build issues with mod_spidermonkey on certain platforms, and
we hope to replace it soon anyway.

Previously we were trying to rely on freeswitch-all providing
freeswitch, but that doesn't seem to work as expected.