lua-utils: correct a type check for a Lua array collection.

Also put there a clarifying comment about the check.
build-sys: Add checks for Debian-packaged lua.

This adds checks for lua5.2 and lua5.1, and keeps the override
available for cases where a specific lua version is needed.
build: change Automake strictness to "foreign".

This removes automake's need to copy standard GNU INSTALL file
when run with --install. Additionally removes INSTALL as we
do not use it in Murphy
docs: generally document compilation in README.md.