def: add a "high" limit for RLIMIT_NOFILE

def: add a "high" limit for RLIMIT_NOFILE

This simply adds a new constant we can use for bumping RLIMIT_NOFILE to
a "high" value. It default to 256K for now, which is pretty high, but
smaller than the kernel built-in limit of 1M.

Previously, some tools that needed a higher RLIMIT_NOFILE bumped it to
16K. This new define goes substantially higher than this, following the
discussion with the kernel folks.