Implement rejection of POSIX collating elements ("[.ch.]" and "[=ch=]"
entirely in the Ragel parser, using the same approach both inside and
ouside character classes.
Fix buggy rejection of [^.ch.], which we should accept as a character
class.
Bring hs_reset_stream(), hs_reset_and_copy_stream()'s functionality into
line with hs_close_stream() by accepting a NULL scratch if and only if
the match callback is also NULL, indicating that no matches should be
delivered.
