Fix minor whitespace issues after "." in manual.

Fix minor whitespace issues after "." in manual.

Be more systematic about using "@." (not ".") at end of sentence that
ends in a capital letter, and about appending "@:" after non-ends of
sentences that end in a lower case letter followed by "." followed by
whitespace.  Omit unnecessary use of "@:" and "@.".  Similarly for "?"
and "!".  Be more consistent about putting a comma after "i.e." and
"e.g."; this is the typical American style and it's easier to code in
Texinfo.

Fixes: debbugs:12973