Apport 2.4

Improvements:
 * apport_python_hook.py: For org.freedesktop.DBus.Error.ServiceUnknown
   exceptions, add a 'DbusErrorAnalysis' field to the report which points out
   whether any .service file provides the service it tried to talk to, and
   whether the processes for those are running. This helps to determine the
   root cause for such errors (missing dependencies, broken .service files,
   talking to the wrong bus, etc.) (LP: #1020572)
 * hookutils.py, attach_alsa(): Use alsa-info.sh when available. Thanks David
   Henningson.
 * Add new "RecoverableProblem" report type for problems which the application
   can handle, but still wishes to notify the user and send a problem report
   about. As an example, the application may wish to notify the user because
   handling the error resulted in degraded functionality. The user interface
   may fail to load items, or the action just performed may not return any
   data. Applications call /usr/share/apport/recoverable_problem with a
   string of arbitrary NUL-separated key/value pairs that are added to the
   report. Thanks Evan Dandrea!

Bug fixes:
 * ui tests, test_wait_for_pid(): Fix eternal hang when running as root.
 * testsuite: Fix ResourceWarnings when running with Python 3.
 * test_python_crashes.py: Fix race condition in timeout test.
 * launchpad.py: Fix setting of 'Medium' importance on duplicate checking.
 * apport-retrace: Fix StacktraceSource generation for relative --cache paths.
 * crashdb.py, check_duplicate(): Do not try to mark a bug as duplicate of
   itself. This can happen when re-processing a previously retraced bug.
 * apport-retrace: Fix UnicodeDecodeError when encountering a non-ASCII source
   code file and running under a non-UTF-8 locale.