Fix svn_io_file_aligned_seek for non-buffered files.  Add test cases to
cover non-buffered files as well.

* subversion/libsvn_subr/io.c
  (svn_io_file_aligned_seek): Re-introduce an "else" that probably got lost
                              as part of some manual conflict resolution -
                              not necessarily on /trunk.

* subversion/tests/libsvn_subr/io-test.c
  (aligned_seek,
   aligned_read_at,
   aligned_read): Add BUFFERED parameter to switch the post-condition
                  checks on svn_io_file_aligned_seek on and off.
  (aligned_seek_test): Add a second access sequence for the same file
                       but in non-buffered mode.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1558484 13f79535-47bb-0310-9956-ffa450edef68