runtime: add throughput counter

throughput_avg is calculated with a wall clock timer over all items produced.
digital: fix false trigger bug in correlate_access_code_tag, add QA code.
grc: fix xterm setting check
grc: catch EOFError on fg exit
Merge remote-tracking branch 'gnuradio-wg-grc/maint_grcwg' into maint
Merge remote-tracking branch 'bistromath/pkt' into maint
Merge remote-tracking branch 'nwest/throughput'
Merge branch 'maint'
grc: On Linux, respect x-terminal-emulator
Merge branch 'maint_grcwg' into master_grcwg
grc: fix port type cache for empty types
Merge branch 'maint_grcwg' into master_grcwg
utils: add error message output to grcc
qtgui: apps: with new use of the Title, the titles provided here just take up extra screen real estate.
blocks: UDP source does not enforce IPv4 anny more
blocks: UDP sink does not enforce IPv4
typos and deletion of never-evaluated code

fixed a few typos in explanatory comments.
Also deleted code in
if 1:
	...
else:
	...
clauses.

Also changed a few [1.0 for i in range(...)] to in-line
[1.0] * (fft_length // 2) for superior readability.
qtgui: remove direct calls to aligned volk kernels; using dispatchers instead.

Addresses problem of using FFTW buffers on AVX machines (when FFTW is not built with AVX).

Addresses Issue #645.
Merge branch 'maint'
Merge remote-tracking branch 'mmueller/ofdm_sync_pn_beautify' into maint