Fix a number of theoretical memory leaks in MythStreamHandler.

Coverity 1213718

There were several points where we'd return early from
ExternIO::Fork() without freeing memory assigned early in the
method. Rather than repeating the same free/delete[] calls at each
point I just moved the assignments down so they occur after all the
possible return points, this works out fine since they weren't
actually used before then.

For this to actually leak in practice the fork and pipe calls would
have to fail which would be a rare event.
Move replex into an external subdirectory.
Fix possible out of bounds array access in mythfilerecorder. Coverity 1213716