XFWM: Hide titlebar when maximized

[ism.a at inode.at]

Hello!

I modified frameTop() so that it also returns 0 if the
CLIENT_FLAG_MAXIMIZED_VERT-flag is set.
This leads to a hidden title bar when a window is maximized.

As I wanted it this way, I implemented it without a way to enable/disable
it (without recompiling).

If you would like something like this in XFWM, I could implement a option
to enable/disable it (e.g. xfwm4-tweaks-settings) and store it in the
configuration too.

If not, I'll just keep it for me the way it is now.
- -
Srdjan Markovic