HEADS UP: Module config change

[Stef Walter]

Some distros have asked if p11-kit could only treat files ending in
'.module' in the modules configuration directories as pkcs11 module
config files.

I'm going to merge this soon, unless there are "stop the presses"
problems. This represents a backwards incompatible change (although
currently just a warning), thus the heads up.

For more details see:

https://bugs.freedesktop.org/show_bug.cgi?id=52158

Cheers,

Stef