Revision 1687070

Following up on r1686554, revert the remaining parts of r1589284.  As we no
longer lock the db/pack-lock in the source repository when hotcopying it,
other relevant changes from r1589284 are no longer necessary.  Doing so
prevents making the non-incremental hotcopy destination openable through
svn_fs_open2() until hotcopy finishes, and that's consistent with how
svn_repos_hotcopy3() currently works.

This changeset restores the hotcopy initialization code to its state in
/branches/1.8.x.  Please note that doing so is going to reintroduce a slight
problem — in 1.8.x hotcopy initialization used to share fs_fs_shared_data_t
instances between the source and the destination.  We actually have a better
way of initializing the shared data (that doesn't reuse it and also doesn't
require writing db/format prior to the moment when a non-incremental hotcopy
is complete), and I am going to implement it in the following commits.

Discussion can be found in http://svn.haxx.se/dev/archive-2015-06/0168.shtml
(Subject: "Re: FSFS7: 'svnadmin hotcopy' requires write access to the
source") and in http://svn.haxx.se/dev/archive-2014-07/0124.shtml
(Subject: "Re: svn commit: r1589284 - [...]").