Change-Id: I5ff18b2768095fb14e7fbece2e756115829abbde

Change-Id: I9bb2cc0cbfac9841b13bed15a474fefb24355cd4

Change-Id: I8e0479b632af3b5ca809aacf955e4be96822ac2c

Change-Id: I06dbc0fdad93c042d783c97378429856bd9111bf

Change-Id: Ia4c9536282af6df3d9d462946dec1d8112459242

The mirror executor will fetch ref updates for repository mirrors.  This
feature is disabled by default and can be enabled by setting
git.enableMirroring=true.  The period between update checks is
configurable, but it is global.  An individual rpeository may not set
it's own update schedule.

Requirements:
1. you must manually clone the repository using native git
   git clone --mirror git://somewhere.com/myrepo.git
2. the "origin" remote must be the mirror source
3. the "origin" repository must be accessible without authentication OR
   the credentials must be embedded in the origin url (not recommended)

Notes:
1. "origin" SSH urls are untested and not likely to work
2. mirrors cloned while Gitblit is running are likely to require
   clearing the gitblit cache (link on the repositories page of an
   administrator account)
3. Gitblit will automatically repair any invalid fetch refspecs with a
   "//" sequence.

Change-Id: I4bbe3fb2df106366ae4c2313596d0fab0dfcac46

Change-Id: I94d4f6146c79541bf8a36e4c3dca1842e46cddd5

This reverts commit f15f17a803.