Lowered wxWidgets version number requirement to 2.8.9.

I incorrectly assumed that since wx 2.8.8 lacked wxAuiToolBar, the entire 2.8.x
series lacked it. In fact in wx 2.8.9 this feature was added.

Thanks to Glenn Rice for spotting this issue.

CMakeLists.txt

@@ -457,8 +457,8 @@ if(NOT DISABLE_WX)
 			ERROR_QUIET
 			)
 		message("Found wxWidgets version ${wxWidgets_VERSION}")
-		if(${wxWidgets_VERSION} VERSION_LESS "2.9.0")
-			message("At least 2.9.0 is required; ignoring found version")
+		if(${wxWidgets_VERSION} VERSION_LESS "2.8.9")
+			message("At least 2.8.9 is required; ignoring found version")
 			unset(wxWidgets_FOUND)
 		endif()
 	endif(wxWidgets_FOUND)