gpsd support

Hi all here I am with the first patch to support gpsd. The new code is used only if libgps is found, otherwise old code is used. There is an issue I had to bypass when integrating old code: the osmocom gps_* funcs have identical names to the libgps api :(. So I had to rename the osmocom gps functions to osmo_gps_*. Unfortunately when using logic names for functions sometimes it creates collisions with other code :). Hope this doesn't create new issues. Tell me if you think it can be considered good from coding approach and if it works :). Cheers Dario.