This prefix prevents the functions from matching the regular expression
of the filter for exported symbols.

* data/dbus/tracker-miner.xml,
* src/libtracker-miner/Makefile.am,
* src/libtracker-miner/tracker-dbus.c,
* src/libtracker-miner/tracker-dbus.h,
* src/libtracker-miner/tracker-miner-dbus.h,
* src/libtracker-miner/tracker-miner-object.c,
* src/libtracker-miner/tracker-miner-web-dbus.h,
* src/libtracker-miner/tracker-miner-web.c: prefix private API with
  "_tracker_"