Add -tx20 option to bin/mspec
Add -tx20 option to bin/mspec

This allows to run the specs in 2.0 mode.

ruby/mspec,iainbeeston/mspec,opal/mspec,nobu/mspec,iainbeeston/mspec,kachick/mspec,kachick/mspec,opal/mspec,eregon/mspec,elia/mspec,ruby/mspec,rubinius/mspec