Fix M4 quoting of section 3.

Fix M4 quoting of section 3.

This fixes M4 quoting of section 3 of the input file, including escape
sequences and character constants.

Tests were added to verify the behavior in section 3 with respect to
quoting. Both escaping of quotes and quoting of potential macro-start
characters are tested. Existing tests were also fixed to account for the new -- and now correct -- behavior. Many tests relied on the old behavior of expanding M4 macros
in section 3.  They needed to be updated for the new behavior.