rename WX_VERSION_FULL back to WX_VERSION

WX_VERSION was renamed to WX_VERSION_FULL for some reason in rev 44731 but
this was a backwards incompatible change as the existing configure scripts
could (and did) use WX_VERSION, so undo this change, at least until someone
finds a worthy reason for it

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48073 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775