Fix up case on all comments to make them more readable. No code changes.

Fix up case on all comments to make them more readable. No code changes.

The all-capsing was a FORTRAN remnant.Also, we change a few FORTRANisms
so they are less confusing in this C context; ".TRUE." and ".FALSE." become
"true" and "false", "MOD" is mapped to % in places tha t are like C expressions
and (usually) "modulo" in places that aren't.