Merge pull request #2 from special/master

[telepathy-gabble] Update to upstream 0.18.1
[telepathy-gabble] Use libiphb to synchronize wakeups

This ensures that the wakeups for IM ping are done simultaniously, and
are scheduled with other system wakeups.
[telepathy-gabble] Change default keepalive interval to 2.5 minutes

Waking up and sending packets at 30 second intervals is unreasonable for
mobile, and seems more frequent than actually necessary. An interval of
150 seconds puts it in the next bracket of iphb wakeups.