Integrate perlio:
Jarkko Hietaniemi [Sat, 11 Nov 2000 15:46:08 +0000 (15:46 +0000)]
[  7641]
Fixup mmap layer by doing mmap() calls on pagesize boundaries.
Also call "Buf" layer directly when unread'ing non-read chars.

p4raw-link: @7641 on //depot/perlio: c3d7c7c914f938b68b6bb6c87dcf5a1eeac909cd

p4raw-id: //depot/perl@7644


Trivial merge