Make parse.h C++ safe by avoiding "or" keyword

Make parse.h C++ safe by avoiding "or" keyword

Fixes for g++ (4.7.2) following compiler errors when fio.h
gets included (e.g. in an external C++ ioengine):

--8<---
[...]
parse.h:31:6: error: expected unqualified-id before ‘or’ token
[...]
--->8---

Signed-off-by: Daniel Gollub <d.gollub@telekom.de>
Updated by me to apply to recent version, and fix gfio usage
of ->or as well.

Signed-off-by: Jens Axboe <axboe@fb.com>