[thrift] add simple test thrift server for evaluation purposes
[thrift] remove stray flag from test
support [many] (str1 str2 ...) format in yarp rpc, for thrift compatibility
[thrift] Added default help function to generated RPC services (addresses issue #118)
Allow use of alternative clocks, system/custom/network.

All YARP's use of time can now be diverted to an arbitrary
provider, including from the network.  ROS-style /clock topic
can be enabled by setting YARP_CLOCK=/clock in the environment.
mark USE_PORT_AUTHENTICATION as advanced, give better error message, fixing #121
Added tab-completion for yarp rpc when Readline library is available (only works properly with Thrift-generated services)