Cover svn_fs_is_txn_root and svn_fs_is_revision_root in our FS tests.

* subversion/tests/libsvn_fs/fs-test.c
  (basic_commit): Check root types before and after the commit.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1633968 13f79535-47bb-0310-9956-ffa450edef68