Fix building xcomposite plugins with pkg-config

wayland-server.h is included in the generated code, therefore
wayland-server has to be added to PKGCONFIG.

Change-Id: I9a0eba7decba8d2db5e5e3de82069976faa24164
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Wayland platform: Do not crash when opening a popup without the mouse

set_popup requires a wl_seat which we will not have if the mouse has
not been touched. Avoid set_popup in this case, otherwise all we get
is a crash.

Change-Id: I591b218c18e3812cdc5fb86e8bf8b92caf64a4f6
Reviewed-by: Andy Nichols <andy.nichols@digia.com>