Patch to use wxGetMouseState

[abligh]

Newer versions of wxWidgets have a wxGetMouseState function. This patch allows this to be used if present (defined by a #define, defaulting to off). If it is present, an additional #define controls whether the wx version is used, or a #include has to be made (because of a backport).

Patch at:
http://www.alex.org.uk/wxAUI/0.9.1/usewxgetmousestate.p

Needs to be applied on top of
http://www.alex.org.uk/wxAUI/0.9.1/mac.p
as it also fixes the Mac version to read a more immediate version of the button state.