Update required wxWidgets to at least 2.9.5.
Update friend declarations to conform to modern standards regarding default arguments.
Workaround for compile error in wxWidgets

The wxWidgets macro wxFinite calls isfinite; on recent C++ compilers
this raises an error, as the more proper call is std::isfinite.
This commit manually redefines this macro in the source files where
it is called; a less than elegant but probably essential solution.