flux: add installed lua paths to env

Prepend:
  $(luadir)/?.lua to LUA_PATH
  $(luaexecdir)/?.so to LUA_PATH

This allows a "side-installed" flux-core to work properly without
relying on finding our lua modules in the system default path.

As an example, for flux-core installed to my $HOME/flux, flux.c sets:
  LUA_PATH=/home/garlick/flux/share/lua/5.1/?.lua;;;
  LUA_CPATH=/home/garlick/flux/lib64/lua/5.1/?.so;;;
cmbd: module name containing "/" is loaded by path

If a module name is specified to cmbd with a / in it, presume that
this is the path to a shared object file in module format and
treat failure to load it as a module as a fatal error.

The old scheme would try to load 'barrier' as a module if it existed
in the current working directory.  Now we would require ./barrier
if that is desired.
flux-module: update module search to match broker
Merge pull request #21 from garlick/flux-config4

misc out of tree/side install fixes