ci: Enable use of precompiled headers by travis-ci

Change-Id: I5221afcc967beeb7baf0a2f68c3fbffff80eaf97
sqlite3: Reverting "dotfile" locking

Now we're back using the normal filesystem locking by default
and using "dotfile" locking only when requested with
``--without-sqlite-locking`` option to configure.

Change-Id: Ic6400151cec64c7c9fa20a6a91ec29251e5b149a