Apport 2.20.2

* problem_report.py: Make assertion of invalid key names more verbose.
 * hookutils.py: Fix generation of valid report key names from arbitrary paths
   in attach_file() and related functions. This will now replace all invalid
   characters with dots, not just a few known invalid ones. (LP: #1566975)
 * problem_report.py: Instead of AssertionError, raise a ValueError for invalid
   key names and TypeError for invalid kinds of values. Thanks Barry Warsaw.
 * Don't ignore OSError in Report.add_gdb_info(), as we do want to fail with an
   useful error message if gdb cannot be called in apport-retrace. Move the
   catching to the UI as not having gdb installed is still fine for reporting
   clients. (LP: #1579949)
 * Show gdb error messages in Report.add_gdb_info() OSError exception when gdb
   fails. (LP: #1579897)
 * hookutils, attach_root_command_outputs(): Return str again, like before
   2.15.2. (LP: #1370259)
 * Stop issuing "set architecture" gdb commands on ARM and Power; these only
   applied to 32 bit platforms and are apparently not needed any more with
   recent gdb versions. (LP: #1585702)
 * Disable report.test_add_gdb_info_abort_libnih test case for now, as libnih
   is broken under current Ubuntu (LP: #1580601)
 * do-release: Drop generation of ChangeLog. Interesting changes are already
   documented here, and the details can be seen in the bzr log.