Set source file when constructing AST nodes

[zirkel]

When the source information is set, the File field is currently left as null. This causes a null pointer exception whenever TASS tries to print the source.

[Stephen Siegel]

I got rid of the null pointer exception in the Source class by checking whether file is null.
But this still has to be fixed.
Is the problem in the ast module, or the Clang module?

[zirkel]

Seems to be at least partially in ast, based on this comment in ast.parser.LeafSourceParser.java:

//FIXME: Actually get file instead of passing in null

[stachnik]

Fixed in rev. 2329