Adding QoS support for Rygel GET requests.

Setting the IP_TOS (DSCP) and SO_PRIORITY socket options for GET-based requests based on the transfer mode of the request.

DSCP values for each transfer mode:
Streaming: 0x28
Interactive: 0x0
Background: 0x8

Adds a dependency on the posix package during vala compilation.
Whitespace fixes
Merge pull request #8 from cablelabs/qos_support

Adding QoS support for Rygel GET requests.