build: package-info: factor the generation of C header.
build: package-info: factor the generation of C header.

	* build-aux/git-version-gen (Rev): Rename as...
	(Revision): this, so that we use the same name inside (the
	key in the hashes) and outside (the output files).
	(generate_header_entry, format_keywords): New.
	(generate_header): Use them.

aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport