clang doesn't like anything but a bare 0 as null (and in some of the
cases, it was quite right: '\0' should not be treated as a null
pointer). And the crashers were just for paranoia and probably aren't
needed any more (kept for now, though).
parser a bit to accomodate this. Backslashes in double quotes are now only
removed if they escape a character that can't be written normally, or
another backslash. Removed start position support from string::findsub
since variable slices can be used instead. Added support for regular
expressions in the form of regex::match, regex::replace, and
regex::extract. Checked in regex.c from GNU regex 0.12 for platforms that
do not have regex functions in their standard library. Two minor changes
were made to this file to fix gcc warnings. Prepared the path transform
function for a change to a filesystem rooted at fs_userpath instead of the
current gamedir, but these changes are commented out pending security
considerations.
