Also, replace OPT_WATERMARK with OPT_MUST_SAVE, which has the opposite
meaning.
Watermarking of aliases does not yet work correctly in this version.
Neither does the "include" command.
Previously, they were reset by smart_config_string(), which was not
called if the value of the option was saved by rewriting an existing
command in elinks.conf. Also, it is better to reset the flags only
after the file operations have actually succeeded.
Previously, ELinks set the OPT_WATERMARK flag in all deleted options
when config.saving_style was 2, thus mostly preventing them from being
saved. This had the unfortunate consequence that if you started with
no elinks.conf, set config.saving_style = 2, deleted some built-in
option (e.g. a URL rewriting rule), saved the settings, and restarted
ELinks, then the built-in option would reappear.
straconcat reads the args with va_arg(ap, const unsigned char *),
and the NULL macro may have the wrong type (e.g. int).
Many places pass string literals of type char * to straconcat. This
is in principle also a violation, but I'm ignoring it for now because
if it becomes a problem with some C implementation, then so will the
use of unsigned char * with printf "%s", which is so widespread in
ELinks that I'm not going to try fixing it now.
