Fix a race condition and pool lifetime issue between the FSFS / FSX'
svn_fs_hotcopy implementation and any other FS API call.

The problem is the access to the shared data struct hash.  New entries
must be allocated in a process-global pool (COMMON_POOL) and any access
to it needs to be sync'ed properly (COMMON_POOL_LOCK).

* subversion/libsvn_fs/fs-loader.h
  (fs_library_vtable_t): Add missing parameters to the hotcopy func.
                         It now is similar to all the other entries.

* subversion/libsvn_fs/fs-loader.c
  (svn_fs_hotcopy2): Update the vtable caller.

* subversion/libsvn_fs_fs/fs.c
  (fs_hotcopy): Update signature and use the extra params to open the source
                repo using the properly synchronizing fs_open.

* subversion/libsvn_fs_x/fs.c
  (x_hotcopy): Same.

* subversion/libsvn_fs_base/fs.c
  (base_hotcopy): Update signature, but we don't need it extra params here.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1589254 13f79535-47bb-0310-9956-ffa450edef68