cmake: cmake doesn't have a FIND command for STRING until 2.8.5, so we're just cehcking for that here before using it.

Using cmake < 2.8.5 will not dedup the cflags, but this is non-critical.
blocks: correcting use of mutexes in file_meta_sink.

the gr::block class has a d_setlock mutex that's appropriate for this use instead of creating another for the child class.
qtgui: fixed a bug in the constellation plots that didn't allow us to reduce the number of samples.
qtgui: replaced use of local mutex with d_setlock from gr::block.

Partial response to issue #706.
trellis: updated examples.

+ Fixed paths to match GNURADIO-3.7.x conventions
+ Fixed errors with dimensionality
+ Changed to QT-widgets
trellis: working on issue to fix locations of fsm files in examples.

+ Workaround for the path problem with cmake to use templates for install
+ GRC blocks now check if FSM_Args are strings and if the file exists
+ Changed example generation with CMake
volk: calling enable_languages here is buggy until 2.8.10. Version checking for that.
trellis: minor fixups to trellis examples so prefix doesn't need to end with '/'.
docs: added some cmake cli flags to better configure the build.
Merge branch 'maint'
Merge branch 'master' into next