Update MINA SSHD to SVN 891122

As of 891122 MINA SSHD the SVN trunk revision has two major fixes
on top of 0.3.0 that we need in Gerrit:

- Revision 890632: allows writes to be sent to the client as soon
  as the packet is full, rather than delaying until all data has
  been fully materialized.  Cloning any reasonably sized project
  without this fix is impractical as the entire project must be
  held in JVM heap memory as a single byte[].

- Revision 891122: fixes the receive socket buffer to be larger.
  Raw push throughput went from <4 MB/s to ~25 MB/s.  Actual push
  throughput is lower due to JGit data stream validation and local
  disk IO, but we were really hurting on upload partly due to this
  really bad raw throughput.

Change-Id: If92198a8c436da3752134764931a85e7efd3bc6f
Signed-off-by: Shawn O. Pearce <sop@google.com>
3 files changed