Merge lp://staging/~seb128/indicator-power/dont-leak-content into lp://staging/indicator-power/14.04

Don't leak the g_file_get_contents value, reported by valgrind

Don't leak the g_file_get_contents value, reported by valgrind

==17468== 4,097 bytes in 1 blocks are definitely lost in loss record 1,921 of 1,924
==17468== at 0x40299D8: malloc (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==17468== by 0x428562F: g_try_malloc (gmem.c:255)
==17468== by 0x426C7CE: g_file_get_contents (gfileutils.c:752)
==17468== by 0x8059DEE: ib_brightness_control_get_value_from_file (ib-brightness-control.c:122)
==17468== by 0x8059E76: ib_brightness_control_get_value (ib-brightness-control.c:140)
==17468== by 0x8057E53: action_state_for_brightness (service.c:473)
==17468== by 0x8057E7A: update_brightness_action_state (service.c:480)
==17468== by 0x80592FF: on_bus_acquired (service.c:526)
==17468== by 0x4143137: connection_get_cb (gdbusnameowning.c:480)
==17468== by 0x40DF294: g_simple_async_result_complete (gsimpleasyncresult.c:777)
==17468== by 0x40DF2FA: complete_in_idle_cb (gsimpleasyncresult.c:789)
==17468== by 0x427C59F: g_idle_dispatch (gmain.c:5250)
==17468== by 0x427F83D: g_main_context_dispatch (gmain.c:3065)
==17468== by 0x427FBE7: g_main_context_iterate.isra.22 (gmain.c:3712)
==17468== by 0x428004A: g_main_loop_run (gmain.c:3906)
==17468== by 0x4372904: (below main) (libc-start.c:260)