Allow FILE * as OsiClpSolverInterface::readLp input to allow e.g. unicode file names on Windows

[christoph-cullmann]

I am using OsiClpSolverInterface to read my LP.

Unfortunately it has only a readLp interface that takes a const char*.

On Windows that will not properly allow to pass unicode filenames.

My fix for this is to just allow to pass some pre-opened FILE handle.

Below my patch for this.

fp_input.diff.txt

Would such a change be acceptable upstream or is there a better solution?

@jjhforrest

[christoph-cullmann]

Thanks for taking care, current master has now the needed stuff!