On the log-addressing branch:  Factor out a function evaluating
the various version compatibility FS configuration parameters.
Use that function in all 3 backends such that all of them handle
all compat options that we have.

Allow for 1.x compatibility only and let the backend select the
FS format based on the minor version.

* subversion/include/private/svn_fs_util.h
  (svn_fs__compatible_version): declare new private API function

* subversion/libsvn_fs_util/fs-util.c
  (svn_fs__compatible_version): implement it

* subversion/libsvn_fs_fs/fs_fs.c
  (svn_fs_fs__create): use the new API

* subversion/libsvn_fs_base/fs.h
  (SVN_FS_BASE__FORMAT_NUMBER): remind people to update *_create upon bump

* subversion/libsvn_fs_base/fs.c
  (base_create): use the new API

* subversion/libsvn_fs_x/fs.h
  (SVN_FS_X__FORMAT_NUMBER): remind people to update *_create upon bump

* subversion/libsvn_fs_x/fs_x.c
  (svn_fs_x__create): use the new API

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-addressing@1511324 13f79535-47bb-0310-9956-ffa450edef68