On the log-addressing branch:  Fix / handle  more compatibility cases.

* subversion/libsvn_fs_fs/fs.h
  (SVN_FS_FS__FORMAT_NUMBER): direct devs to svn_fs_fs__create
   in case of format bumps

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__create): reject 1.0 compatibility;
                       fix format version used for 1.8 compat

* subversion/libsvn_fs_fs/fs.c
  (initialize_fs_struct): initialize / default to "phys addressing"

Suggested by: danielsh

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-addressing@1509695 13f79535-47bb-0310-9956-ffa450edef68