prevent main loop recursion
cleaner weak ref management
add URI validation for file://
Use specific background task for HTTP transfers, otherwise the channel might hang when an iOS app goes into background
Use background task names when possible (ios7+) and use better names for them
replace fatal asserts with conditionnal check
Fix bug of connection timeout not happening on TLS channel.

The object-oriented architecture was not used correctly for the TLS channel. The call to belle_sip_channel_set_socket was reinitializing the belle_sip_source_t and so erasing the timeout value initialized by stream_channel_connect.
The fix is to just replace the notify callback (that was the only goal of the call to belle_sip_channel_set_socket).
Also added a unit test to check this.
fix host test check
make sure uri without host are valid
rework generic uri file:///
Fix bug 0001348: Incorrect handling of DNS SRV results.
Merge remote-tracking branch 'source/master'