Fix a potential memory leak.

https://github.com/acpica/acpica/pull/6
Import ACPICA 20130418.
mostly whitespace changes:
- remove vestiges of the old memory allocator
- clean up some comments
Initialise the chainmask fields regardless of whether 11n support
is compiled in or not.

This fixes issues with people running -HEAD but who build modules
without doing a "make buildkernel KERNCONF=XXX", thus picking up
opt_*.h.  The resulting module wouldn't have 11n enabled and the
chainmask configuration would just be plain wrong.
Merge ACPICA 20130418.
Expose CAM_BOOT_DELAY as a kernel conf item now.

This allows users who boot without loader to adjust their environments
around slightly buggy or slow hardware.

PR:	kern/161809
Submitted by:	rozhuk.im@gmail.com
MFC after:	2 weeks
Add note about fagility of the clang upgrade process.