digital: fixes for SNR ests.

set_history: you keep using that word. I do not think it means what you think it means.
Merge branch 'maint'
docs: adds protection from generated files of components not configured.

Also removes a couple warnings in generating docs.
Merge branch 'master' into next

Also updating to make changes in maint/master to next.

Conflicts:
	docs/doxygen/CMakeLists.txt
	gnuradio-runtime/lib/pmt/CMakeLists.txt
	gr-digital/lib/digital_impl_mpsk_snr_est.cc
	gr-digital/lib/digital_mpsk_snr_est_cc.cc
	gr-digital/python/qa_mpsk_snr_est.py