update hooks: smooth out the dev-vcs migration
update hooks: smooth out the dev-vcs migration

Not everyone got a smooth migration for git/subversion from dev-util
to dev-vcs, so add a hook to manually unmerge the old versions.  The
newer packages should recover gracefully after that.

BUG=chromium-os:24360
TEST=build_packages ran ver 23 upgrade and continued on

Change-Id: I0b56f0f0a8b8a7ebd64a4a664e5524f0b7828791
Reviewed-on: https://gerrit.chromium.org/gerrit/13663
Reviewed-by: Doug Anderson <49983c4a76b998672954ed5edf4a62db4a336502@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Commit-Ready: Doug Anderson <49983c4a76b998672954ed5edf4a62db4a336502@chromium.org>

mischief/scripts,andrejro/coreos--scripts,bcwaldon/coreos-scripts,marineam/coreos-scripts,sigma/coreos-scripts,fivethreeo/scripts,gtank/scripts,crawford/scripts,vmware/coreos-scripts,BugRoger/scripts,crawford/scripts,zhang0137/scripts,gtank/scripts,glevand/coreos--scripts,mischief/scripts,glevand/coreos--scripts,endocode/scripts,mjg59/scripts,mjg59/scripts,marineam/coreos-scripts,smilart/scripts,nicescale/scripts,zhang0137/scripts,marineam/coreos-scripts,vmware/coreos-scripts,bcwaldon/coreos-scripts,trnubo/scripts,vmware/coreos-scripts,trnubo/scripts,andrejro/coreos--scripts,mischief/scripts,endocode/scripts,BugRoger/scripts,zhang0137/scripts,smilart/scripts,smilart/scripts,gtank/scripts,nicescale/scripts,coreos/scripts,crawford/scripts,endocode/scripts,sigma/coreos-scripts,fivethreeo/scripts,mjg59/scripts,trnubo/scripts,sigma/coreos-scripts,andrejro/coreos--scripts,bcwaldon/coreos-scripts,fivethreeo/scripts,coreos/scripts,BugRoger/scripts,nicescale/scripts