tcp_usrreq: fix the previous - the assert is still not true (but PRU_SENSE
case will handle it); eventually, pr_usrreq should not be called without
PCB attached.
create /tmp at bootstrap, default TMPDIR used by some programs (e.g. ed)
Some small changes in preparation for a bigger change.

- typedef for ABC variables and MAX_ABC_LENGTH constant,
- cast pc->k to uint32_t in more places,
- whitespaces.
Add uao_set_pgfl to limit a uvm_aobj's pages to a specified freelist.

Brought up on tech-kern:

https://mail-index.netbsd.org/tech-kern/2014/05/20/msg017095.html
gcc-4.8.3 out.
Put missing END() markers to set ELF symbol size.
Indent.
Put missing END() markers to set ELF symbol size.
Put missing END() markers to set ELF symbol size.
Define TTY_ALLOW_PRIVATE in tty.c, tty_pty.c, and tty_conf.c.

These modules are the core of the tty code that in the long term needs
access to struct tty. (It may be that in the future this can be cut
back to just tty.c; we'll see. For now I'll settle for keeping drivers
out of struct tty.)
Use uintptr_t so this file can be compile-tested on foreign arches.
Use accessor functions for the tty's table of control characters.
(at least from outside the core tty sources)

Move some xon/xoff code from net/ppp_tty.c to kern/tty.c.
fix build for _KERNEL