Revision 1498089

On the fsfs-format7 branch: First step in creating the new FSX backend.
Copy libsvn_fs_fs to libsvn_fs_x, rename fs_fs.* to fs_x.* and update
the build config.

* subversion/libsvn_fs_x: new, copied from ../libsvn_fs_fs
* subversion/libsvn_fs_x/fs_x.c: renamed from ./fs_fs.x
* subversion/libsvn_fs_x/fs_x.h: renamed from ./fs_fs.h

* subversion/libsvn_fs_x/cached_data.c,
  subversion/libsvn_fs_x/caching.c,
  subversion/libsvn_fs_x/dag.c,
  subversion/libsvn_fs_x/fs.c,
  subversion/libsvn_fs_x/hotcopy.c,
  subversion/libsvn_fs_x/lock.c,
  subversion/libsvn_fs_x/low_level.h,
  subversion/libsvn_fs_x/pack.c,
  subversion/libsvn_fs_x/rep-cache.c,
  subversion/libsvn_fs_x/revprops.c,
  subversion/libsvn_fs_x/revprops.h,
  subversion/libsvn_fs_x/transaction.c,
  subversion/libsvn_fs_x/tree.c,
  subversion/libsvn_fs_x/util.c,
  subversion/libsvn_fs_x/verify.c: update #includes