Rename readme file in languages directory to regenerate_po.sh

The packagers of the various linux distributions told us last release,
this text file has warnings as the +x bit is set. To circumvent this
warning for packagers, we'll rename the file to what it actually does.
Add a .gitattributes file

This file can be used to tell git about certain attributes for files.
The current entries basically tell git to exclude files, when generating
the release tar-ball with
	git archive --format=tar.gz master > ../flare_release.tar.gz
Merge pull request #814 from stefanbeller/release_preparations

Release preparations: Rename languages/readme and ignore files when creating release tarball