El-get check mode and minor doc fixes.

The major change is the second commit f1c742d.  It adds a `special-mode` for the `el-get-check-recipe` buffer which, e.g., allows to quit the buffer using q or rerun the test using g.

The first commit contains a few docstring and line length fixes.  The third change adds a description of `test-recipe.sh` to the info manual.