Bogus /usr/bin/... paths in Lua module search

[alerque]

While commenting on an issue over on ZeroBraneStudio I did the sensible thing and actually looked at the final search path being used by SILE to load anything.

$ sile -e 'require("bogus")'

The result for my system's installed sile includes a bunch of bogus paths in /usr/bin/...,

It looks like maybe this line is to blame:

sile/sile.in

Line 22 in c4e040c

extendPath("@SILE_PATH@")

SILE_LIB_PATH probably belongs, but SILE_PATH probably does not. This probably snuck in here because it makes sense for using SILE uninstalled from a project directory (git checkout or tarball extract) as ./sile. In that case it would be needed ... but perhaps we need to a different way to solve that rather than wasting time looking at reams of bad paths (this causes hundreds of useless filesystem operations, something that is notorious for being a large part of why LaTeX –and elpecially LuaLaTeX) is so slow).