Add the 'vos endtrans' command

Add the 'vos endtrans' command

Add a command to vos to explicitly end volume transactions. These can
happen if (for example) we segfault or the user ctrl-C's in 'vos'
before/after a volume operation, but before we AFSVolEndTrans.

Change-Id: Ie34ee1fdff917b56900f456c7cf8b1329533a7da
Reviewed-on: http://gerrit.openafs.org/870
Reviewed-by: Dan Hyde <drh@umich.edu>
Reviewed-by: Alistair Ferguson <alistair.ferguson@mac.com>
Tested-by: Alistair Ferguson <alistair.ferguson@mac.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>