store errno on the private process stack so its always per process
and not just per memory space. errno itself becomes a macro
dereferencing int *_errnoloc; which is initialized from main9.s
pointing to the private stack location.
various fixes in programs that just imported errno variable with
"extern int errno;" instead of including <errno.h>.
add PASS_MAX to limits.h for ape, and make getpass respect it. also increase the size of
the maximum passwords (we use long ones at work). Needed for native port of SVN (in progress).