Merge branch 't/misc'

Various fixes, improvements, cleanups. Cooking since 2014-02-22.

* t/misc: (29 commits)
  build: Don't link with -lreadline if readline was not found.
  audiod: Skip NULL pointer check in compute_time_diff().
  audiod: Make compute_time_diff() return void.
  com_stat(): Remove pointless uptime variable.
  gcrypt: Fix gcc warning on Ubuntu Lucid.
  flac: Try to link also without -logg.
  version.c: Fix comment of version_single_line().
  doxygen: Expand all macros, in particular config.h.
  recv_common.c: Improve documentation of check_receiver_arg().
  audiod: get_time_string() comment fix.
  configure: Really print opus audio file handler if opus lib was found.
  Overhaul doxygen main page.
  afs.h: Don't try to list all supported audio formats.
  Change copyright year to 2014.
  Add link to sideband.h in doxygen main page.
  Doxify error2.c and add GPL header.
  Add -Wdeclaration-after-statement.
  Add some missing includes.
  Makefile.real: Add clean2 to the list of phony targets.
  mood.c: Fix a trivial whitespace issue.
  ...