Fix wikiversions compilation problem

The inplace chmod introduced in If3bd73f fails when executed by a user
in the wikidev group who doesn't actually own the file. Use the same tmp
file + rename method used by the cdb compilation to avoid this.

Also renames scap.tasks.compile_wikiversions_cdb to
scap.tasks.compile_wikiversions and updates the doc string.

Change-Id: Ice6d60de319368230c015eb28630cd8904236771