Add support for RLIMIT_NPTS to limits(1).

Add support for RLIMIT_NPTS to limits(1).

After the MPSAFE TTY import we support an additional rlimit, called
RLIMIT_NPTS. This limit allows you to cap the amount of pseudo-terminals
allocated by one user.

We forgot to add support for this limit to limits(1), which means it
crashed. Add the proper bits to make it work like it should.
Unfortunately not all shells actually implement the RLIMIT, so
unfortunately I suspect it to be broken with certain shells.

Submitted by:	Yuriy Tsibizov <yuriy tsibizov gfk ru>