new support for Raspberry Pi B+

[draymond at FoxValley.net]

It seems that "portsnap fetch update" is a consistent way to generate  
a panic.  I have now seen panics with all four of my SD cards on two  
different Raspberry Pis, and with three different power cables.  All  
occurred while running at low speed for SD (25MHz) on r274416.  Here  
is the latest panic:


ssh output:
-----------
root at raspberry-pi:~ # time portsnap fetch update
Looking up portsnap.FreeBSD.org mirrors... 7 mirrors found.
Fetching public key from isc.portsnap.freebsd.org... done.
Fetching snapshot tag from isc.portsnap.freebsd.org... done.
Fetching snapshot metadata... done.
Fetching snapshot generated at Mon Nov 24 17:13:37 MST 2014:
a9871e18baf0354c1d0795484a204847f79729af04cbfe100% of   70 MB  740 kBps 01m37s
Extracting snapshot... done.
Verifying snapshot integrity... done.
Fetching snapshot tag from isc.portsnap.freebsd.org... done.
Fetching snapshot metadata... done.
Updating from Mon Nov 24 17:13:37 MST 2014 to Mon Nov 24 21:03:40 MST 2014.
Fetching 4 metadata patches... done.
Applying metadata patches... done.
Fetching 0 metadata files... done.
Fetching 66 patches.
(66/66) 100.00%  done.
done.
Applying patches...
done.
Fetching 20 new ports or files... done.
Removing old files and directories...


console output:
---------------
dev = mmcsd0s2a, block = 343613, fs = /root/crochet/work/_.mount.freebsd
panic: ffs_blkfree_cg: freeing free frag
KDB: enter: panic
[ thread pid 8 tid 100056 ]
Stopped at      $d:     ldrb    r15, [r15, r15, r15, ror r15]!
db>


Ian, you mentioned that you thought this looked like a memory  
corruption similar to the issues reported on Wandboard.  I have been  
reading those threads but I don't fully understand what is the issue.   
Can you clarify?  I also saw some discussion about some new changes  
currently under testing and planned for release.  Are these expected  
to resolve the memory corruption?  What is the root cause and is the  
problem present in all builds or just recent builds?