[RFC] SysV SHM on 64-bit platforms

[Jung-uk Kim]

While I was working on kern/113218, I realized it is a bigger problem 
than I originally thought:

http://www.freebsd.org/cgi/query-pr.cgi?pr=113218

Because fixing this PR breaks ABI, I had to make compat shims.  But 
the question is which branch to break?  Since we are very close to 
7.0-RELEASE, the question became more complicated.  A lot of people 
are asking me to fix this PR because it is much needed fix for large 
database installations, so I have to make a quick decision. :-(

I think I have four options (with corresponding patches):

- Option 1: HEAD.

HEAD:		http://people.freebsd.org/~jkim/shmmax8o.diff

- Option 2: HEAD and RELENG_7.

HEAD:		http://people.freebsd.org/~jkim/shmmax8c2.diff
RELENG_7:	http://people.freebsd.org/~jkim/shmmax7s2.diff

- Option 3: HEAD, RELENG_7, and RELENG_7_0.

HEAD:		http://people.freebsd.org/~jkim/shmmax8c.diff
RELENG_7:	http://people.freebsd.org/~jkim/shmmax7s.diff
RELENG_7_0:	http://people.freebsd.org/~jkim/shmmax70.diff

- Option 4: Don't do anything ATM.  Break it with ipc_perm later.

FYI, fixing ipc_perm is a lot more complicated and very intrusive.

What do I do now?  Do I have any other options?

Jung-uk Kim