regcomp.c: White-space only

Properly indent 9 lines.  This makes it easier to see the logic flaws to
be fixed in the next commits.
regcomp.c: Process all POSIXes in [...] under /l

Commit 31f05a37 introduced a regression in which if you have something
like /[\s\d[:punct:]/, all but the final class were ignored.  This was
due to initialization happening every time through the loop, instead of
the first time needed.