[O] Line with single character : as valid literal area

[Jeff Kowalczyk]

Feature request to add ^:$ as valid literal area. I would prefer to call
delete-trailing-whitespace on org buffers before save and git check-in:

: >>> 2+2
: 4
:(EOL)

I don't yet use all of org syntax, but this is the only part of my own outlines
that I've made invalid by deleting trailing whitespace.

To those with knowledge of the org parser grammar, is this possible?

Thanks,
Jeff