Instead of nesting, try to exit as soon as possible in case of errors.
Also make sure to tell the caller whether the call succeeded and a
fallback should be attempted.
One some systems (tested with Gnome 3 on Arch Linux) the current method
of using `xdg-screensaver` to suspend the screensaver does not work.
Instead, using DBus to issue an `Inhibit` request is recommended.
The request returns a cookie that needs to be re-used to un-inhibit the
screensaver later. Additionally if the DBus connection is closed the
current inhibition is discarded. Thus, the DBus connection needs to stay
connected for the duration of the screenshot inhibition.
The code is heavily inspired from the [SDL 2.x
code](http://hg.libsdl.org/SDL/file/default/src/core/linux/SDL_dbus.c#l172).
I didn't call the SDL 2 code though since this it to fix the issue with
the GL driver, and I assume one would want to have screensaver inhibited
even when SDL 2 is not available (but GL is).
I've set "WIP" because:
* I haven't done C in a long time so my code is probably not great
* There's a dependency on DBus which I don't know is acceptable or
not
* I've put my code where I could to check it works, but `x11_common` may
not be the best place
* The code need and "init" and "deinit" kind of method as it needs to
initialise the DBus connection, and on deinit close it properly. I've
used `x11_connect` and `x11_window_destroy` but they don't sound like
the best choices.
* I'm a bit unclear as to what happens when "suspend screensaver" is
ticked on/off in the menu. This doesn't seem to call
`x11_suspend_screensaver` everytime, so I'm not sure if there's a hook
somewhere (as disabling screensaver suspend in the menu should cause a
DBus unhinibit request to be sent).
* Should I just call the SDL 2.x code (meaning that the GL driver would
depend on SDL 2.x at runtime)?
So, first of all are you ok with the approach, and if yes I'd gladly get
feedback about the code, how to architecture it and the best place to
put it.
Thanks!
For some reason, OriginalHistory blit happened inside a render pass.
Also add more TRANSFER_SRC_BIT caps to images as they might have to be
copied to history.
