Prefer using the POSIX constant PATH_MAX instead of the legacy BSD
derived MAXPATHLEN. The necessary includes for MAXPATHLEN and PATH_MAX
are <sys/param.h> and <limits.h>, respectively.
Signed-off-by: Felix Janda <felix.janda@posteo.de>
Tested-by: Yegor Yefremov <yegorslists@googlemail.com>