Use absolute path when compiling files

[hiker]

A very minor improvement:

ATM a relative path is used for the source file when calling the compiler (i.e. only the file name). This works because the subprocess is changing into the right directory when executing the compiler.

But this makes it harder to verify if the right files are compiled (e.g. I spent some time debugging based on the assumption it would compile a different version of the file, since I wasn't sure of the implicit 'chdir' done), and also does not allow you to simply copy&paste the compilation line (e.g. for testing).

I have a patch for this ready (but apparently can neither assign this to me, nor set a label :) ).