This makes math-extern a bit more visible and re-organizes the Edit->Math submenu.
I guess the result of the configure stuff should be used to disable the math-extern menu entries if no CAS was found, but I do not know how to do it. Introduce new boolean variables in lyxrc.[Ch]? Andre' -- Those who desire to give up Freedom in order to gain Security, will not have, nor do they deserve, either one. (T. Jefferson)
