core: adding gr_random_pdu message passing block

Conflicts:
	gnuradio-core/src/lib/general/CMakeLists.txt
	gnuradio-core/src/lib/general/general.i
core: gr_socket_pdu missing iostream
block: file_source_impl missing mutex include
core: removed redundant test settings
Merge branch 'maint'
digital: made the demod examples clearer
grc: Fixed Bug #485 by gracefully exiting when user sets GR_DONT_LOAD_PREFS=1 GRC_BLOCKS_PATH=
wxgui: dead code removal and formatting cleanup
core: added operator == for tags
core: added remove_tag_item()
Merge branch 'maint'
wxgui: implement persistence without using glAccum
Merge remote-tracking branch 'mbant/demod_examples'
Merge remote-tracking branch 'mbant/fix485'
Merge remote-tracking branch 'mbant/equal_for_tags'
grc: fixed problem of GRC_BLOCKS_PATH not being set in Windows
Merge branch 'maint'
digital: Updated constellation_receiver_cv documentation.
digital: Updated pfb_clock_sync grc xml file.
digital: Fixed bug in digital_bert_rx.py (thanks Charles Ru)