Add --compile and --lint arguments.

--compile compiles the script before doing anything else.

--lint is a backwards compatable way of invoking the lint
command. We've been parsing it as an argument for a while, but it
didn't work.
sl2: Make the version of screen language used configurable.

For now, this is controlled by an environment variable.
Do not attempt to resize a 0-width or 0-height displayable.

This prevents a divide-by-zero.
A regression prevented insensitive buttons from working.