Implement the ability to read data from a repos file:
Implement the ability to read data from a repos file:

(svn_fs_file_contents):        implement
(txn_body_get_file_contents):  new machinery for above.
(file_contents_baton_t):       new machinery for above.

Also, stop calling open_path in svn_fs_apply_textdelta:

(txn_body_get_source_stream):  call get_dag instead of open_path.
(txdelta_baton_t):  lose parent_path, gain a dag_node_t instead.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion