blocks: adding ability to set a key filter in tag_debug block.
blocks: adding message ports to repack_bits for setting input and output values with messages.
blocks: added message handler to reset symbol map of chuncks_to_symbols.
digital: adding message handler to send a new constellation to the constellation_receiver as a message. Also adds ControlPort interfaces.
digital: adding ControlPort interfaces to the costas loop (also formatting tabs to spaces).
digital: adding a correlate-and-sync block.

This block takes a preamble, finds a correlation, calculates the timing and phase offset estimates from it and passes these on as tags to follow-on blocks (like a clock_sync and costas_loop or constellation_receiver block).
digital: improved handling of data using forecast function in the pfb_clock_sync.
digital: costas_loop looks for 'phase_est' tags and resets its phase estimate based on this. pfb_clock_sync_ccf does the same with the 'time_est' tag to initialize loops on a burst.

pfb_clock_sync_ccf has the same modifications as the _fff block in the last commit.
runtime: executor uses information about the numer items produced/consumed to update the relative rate. This makes sure tags are being propagated by all blocks correctly. Needed for pfb_clock_sync to use the correlate_and_sync block's tags.
qtgui: time sink plots (complex and float) display tags on the sample they were received on. Displayed as "key: value".

Conflicts:

	gr-qtgui/examples/CMakeLists.txt
qtgui: adds trigger capabilities to time sink.

Mode, slope, level, delay, and channel settable in GRC and through interactive menu.
runtime: for blocks with a group delay, tag location should be moved according to the delay. Since group delay is often unknown, we have added a new function set_group_delay to allow the user to set the value once delay is calculated.

Also added ability to set the tag propagation delay, which is required for how the blocks::delay works.
Updated some blocks for the group_delay concept.

filter: FFT and (decim/interp) FIR filters can set through GRC.

blocks: delay block's group delay is fixed to the delay value.

qtgui: time sinks history is related to the group delay for displaying tags.
qtgui: added ability to trigger off a tag with a specific key.
qtgui: fixed histogram autoscaling features. Added example script.
qtgui: fixing variable names to make it more like the rest of the code.
digital: cleaning up pfb_clock_sync and fixing a segfault in the ccf version.
filter: new taps() and ntaps() accessors to fft_filter kernels.
qtgui: fixed bug with setting delay.
digital: pfb_clock_sync: normalizing differential taps for each channel.