Declare methods protected instread of private

[NicolasAnquetil]

In FrontEnd, and FortranStream, many methods are declared private.
This prevents anybody from inheriting from these class and extending their behaviour.

For example, I wanted to have a FrontEnd that could parse from a String (for example using ByteArrayInputStream or something similar). One solution would be to inherit from these classes and change some of their methods. Because they are private, this is not possible and the only solution is to copy/change a lot of code :-(