Set overall maximum number of lines to scan.

dtrt-indent-max-relevant-lines becomes dtrt-indent-max-lines, because
otherwise some very large files take a long time to scan; with an
overall maximum, the maximum relevant number is no longer needed.
Fix some skip patterns

Some were \\\\. that is, literally, \\., two backslashes followed by a
character. This is not what was meant, as far as I can see, and was
contradicted by other languages with \\. that is literally, \., which
have the same quoting rule.