Added mspec help options_or_mode, moved fmode helper.
Use options_or_mode in new_fd and new_io helpers.
Add -tx18 option to bin/mspec

This allows to run the specs in 1.8 mode if you are
using 1.9 mode by default.
Add -tx20 option to bin/mspec

This allows to run the specs in 2.0 mode.
Add -tx18, -tx19 and -tx20 options to the docs
Add a new helper to spec.

pack_int helper added.
This new helper is used in library/socket/basicsocket/setsockopt
spec.
Removed --spec-debug because ruby_debug is always broken.