Commit f975858e86 removed the NULL check in g_cancellable_cancel() by
accident which makes it crash when called with NULL.
Add the check back and add a test so this doesn't happen again.
Fixes#1710
Very many testcases, some GLib tools (resource compiler, etc) and
GApplication were calling g_type_init().
Remove those uses, as they are no longer required.
https://bugzilla.gnome.org/show_bug.cgi?id=686161
The test was assuming that all cancelled ops would finish within a
certain amount of time, but this often failed under valgrind. Instead,
just run the loop until all of the ops have actually finished.
https://bugzilla.gnome.org/show_bug.cgi?id=682560
* Update documentation to note that GCancellable can be used
concurrently by multiple operations.
* Add documentation to g_cancellable_reset that behavior is
undefined if called from within cancelled handler.
* Add test for multiple concurrent operations using the same
cancellable.
https://bugzilla.gnome.org/show_bug.cgi?id=656387
