Cleanup self._signal_recipients_by_object_path (fd.o #17551)

In Connection, add_signal_receiver adds object paths to
self._signal_recipients_by_object_path and they are not cleaned by
remove_signal_receiver.

As a result self._signal_recipients_by_object_path keeps growing indefinitely.

This seem to work for me. I know very little about dbus-python though, so I
could very well be doing it wrong.

https://bugs.freedesktop.org/show_bug.cgi?id=17551
https://bugs.freedesktop.org/attachment.cgi?id=18857

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Start development for 0.83.1
Merge branch 'mpg'
NEWS: mention mpg's bugfix
Message.set_sender: allow org.freedesktop.DBus

I found Message.set_sender method only accepts unique bus name. But in
my project, I need implement a simple dbus daemon, it need set the sender
as "org.freedesktop.DBus".
Update NEWS again
fd.o #15013: expose dbus.lowlevel.MESSAGE_TYPE_SIGNAL and friends
tests/cross-test-*: don't use deprecated sets module

set() has been a built-in since 2.4, and we don't support older versions.
fd.o#21172: avoid DeprecationWarning with Python 2.6
Use git log rather than git-log, to support distcheck with modern git
Ignore generated files from newer libtool
Prepare version 0.83.1
Revert "Prepare version 0.83.1"

This reverts commit a63043f262e8938affe515faa145d0f619b9fae6.
Fix signature and return value of Connection_tp_init (oops)
Support silent rules if automake >= 1.11
Require a halfway modern Automake
Use telepathy-glib's macros for desirable and undesirable compiler warnings
Prepare version 0.83.1

Second try :-)
Start 0.83.2
Fixed typo in dbus/bus.py where list_activatable_names would call org.freedesktop.DBus.ListNames instead of org.freedesktop.DBus.ListActivatableNames

Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>