Previously, `mrsh` automatically enabled support for `readline` if it
was detected as installed. However, linking against `readline` currently
doesn't work, so disable it completely instead.
Also removes mrsh from the list of ports missing descriptions. I tried
to be descriptive about the patches, but as I picked this port up from
someone else, I'm not 100% sure how to best explain the patches.
We may need entries with spaces in makeopts, installopts, and
configopts, and at that point we should also convert depends and
auth_opts to avoid confusion.
