Match less of the MacPorts interactive prompt.
Match less of the MacPorts interactive prompt.

- Per @jc00ke, we will not use the semantic version from the interactive
  prompt to anchor the validation.
- Switch to a fixed-string match instead of a regex for performance.
- Relevant comments:
    - <https://github.com/rubinius/rubinius/pull/3298#issuecomment-71936048>
    - <https://github.com/rubinius/rubinius/pull/3298#issuecomment-71940623>

digitalextremist/rubinius,Wirachmat/rubinius,ngpestelos/rubinius,benlovell/rubinius,digitalextremist/rubinius,benlovell/rubinius,digitalextremist/rubinius,kachick/rubinius,benlovell/rubinius,dblock/rubinius,jemc/rubinius,mlarraz/rubinius,digitalextremist/rubinius,digitalextremist/rubinius,benlovell/rubinius,dblock/rubinius,ruipserra/rubinius,mlarraz/rubinius,jemc/rubinius,mlarraz/rubinius,digitalextremist/rubinius,dblock/rubinius,Azizou/rubinius,ruipserra/rubinius,jemc/rubinius,mlarraz/rubinius,heftig/rubinius,jsyeo/rubinius,jemc/rubinius,sferik/rubinius,kachick/rubinius,sferik/rubinius,kachick/rubinius,Wirachmat/rubinius,kachick/rubinius,dblock/rubinius,dblock/rubinius,benlovell/rubinius,heftig/rubinius,Azizou/rubinius,sferik/rubinius,Azizou/rubinius,ngpestelos/rubinius,sferik/rubinius,ruipserra/rubinius,ruipserra/rubinius,heftig/rubinius,ngpestelos/rubinius,dblock/rubinius,jsyeo/rubinius,jsyeo/rubinius,ngpestelos/rubinius,dblock/rubinius,Wirachmat/rubinius,ngpestelos/rubinius,ruipserra/rubinius,Wirachmat/rubinius,heftig/rubinius,heftig/rubinius,ruipserra/rubinius,jsyeo/rubinius,jemc/rubinius,Azizou/rubinius,sferik/rubinius,ngpestelos/rubinius,ngpestelos/rubinius,ruipserra/rubinius,kachick/rubinius,heftig/rubinius,sferik/rubinius,benlovell/rubinius,jemc/rubinius,mlarraz/rubinius,kachick/rubinius,Wirachmat/rubinius,mlarraz/rubinius,jsyeo/rubinius,benlovell/rubinius,Wirachmat/rubinius,Azizou/rubinius,jemc/rubinius,mlarraz/rubinius,sferik/rubinius,heftig/rubinius,Azizou/rubinius,jsyeo/rubinius,digitalextremist/rubinius,jsyeo/rubinius,Azizou/rubinius,kachick/rubinius,Wirachmat/rubinius,kachick/rubinius