[master] Fix problems with translatable strings

[David Shea]

Not every string is translatable, and some translatable strings require some
extra information to make any damn sense to the translators. gettext is
configured to include any comment that begins with TRANSLATORS: in the .pot
file, so use that.

In the bug fixed in patch #2 (854226), the translator is actually asking for
gettext context strings, claiming that 'c' is being used as an input string for
both "close" and "continue". It doesn't look like that's actually the case, or
isn't anymore, but either way python still doesn't have pgettext support, so I
just added some comments instead so that whoever gets asked to translate "c"
gets a hint as to what that actually means.

There is very likely more problems than just these.