Implement window gravity in ConfigureRequests (FS#1137)

Previously, awesome didn't move windows when they sent a ConfigureRequest (and
it also shrunk them by the size of titlebars, before it forgot to add these).
This commit adds proper gravity support to ConfigureRequest handling.

This was tested with test-gravity from metacity (in src/wm-tester).

Signed-off-by: Uli Schlachter <psychon@znc.in>
awful.tooltip: Set the bg color correctly (FS#1148)

Well, whoops. There is no .bg property on wiboxes for quite a while already, it
is now a :set_bg member function.

Signed-off-by: Uli Schlachter <psychon@znc.in>
lua: Print traceback on startup errors

We do some special magic so that we can have tracebacks on errors messages.
However, the code for parsing the rc.lua called it without this magic and thus
errors didn't have tracebacks.

This is bad, because if something goes wrong in e.g. wibox.widget.textbox, you
don't really have any clue where this error is coming from.

Fix this by adding our "print traceback on error"-magic here, too.

Signed-off-by: Uli Schlachter <psychon@znc.in>
honor appended -c option for --check

Signed-off-by: Uli Schlachter <psychon@znc.in>
Merge branch 'master' of git://git.naquadah.org/awesome into split_screen