grc: option to hide disabled blocks
grc: honour order of block paths, print them out on startup, override hier block and pref file path with GRC_HIER_PATH & GRC_PREFS_PATH
grc: nicer output of blocks paths and prefs file
Fix inconsistent naming and docstring

(1) In the XML files, all keys except "log" are used as parameter names.
(2) Most files use the parameter name "log" to flip logging.
    So change the ones that use "logging" or "debug" to "log".
(3) packet_mod constructor does not have the argument payload_length.
(4) Add missing args to some docstrings
(5) Resolve inconsistency between gmsk_demod code and doc
socket_pdu: fixed resolver issue by applying same resolver as in udp_sink.

Basically a version of http://gnuradio.org/redmine/issues/613 reported
by Alex Weihkopf in socket_pdu.
Patch is the same.
added subtraction and addition to time_spec_t
documentation: Bit handling gotchas explained
Merge remote-tracking branch 'gnuradio-wg-grc/grc_hide_disabled_blocks'
Merge remote-tracking branch 'gnuradio-wg-grc/grc_block_and_prefs_path'
Merge remote-tracking branch 'bolin/master'
Merge remote-tracking branch 'mmueller/socket_pdu_fix_resolver_issue'
Merge remote-tracking branch 'mmueller/gr_uhd_time_spec_t_fix'
Merge remote-tracking branch 'tkuester/documentation'