lua pkgconfig file handling

[Thomas Klausner <tk%giga.or.at@localhost>]

Hi!

At least one package, wm/notion, tries to find the current best
available lua version by running "pkg-config lua-5.2", "pkg-config
lua-5.1", and "pkg-config lua" (with additional flags).

This matches what is installed by the packages. However, the pkgsrc
buildlink3.mk files for the lua packages rename all the packages' pc
files to lua.pc, which breaks this (in my eyes entirely reasonable)
detection method.

I'm not quite sure why the buildlink3.mk file even does that. Since
upstream lua provides the files under the names above, why does pkgsrc
unify them this way?

Alternatively, if there is a good reason to keep this, we could
replace it by linking lua-5.x.pc to lua.pc, in other words, provide
both of them.

Comments?
 Thomas