Remove rhizome_read_manifest_file()

Replace with memcpy() followed by rhizome_manifest_parse()
for memory buffers

Replace with rhizome_read_manifest_from_file() for files
HTTP server response codes 408, 409
Use manifest 'has_id' consistently
Make rhizome_manifest_pack_variables() static
New enum rhizome_add_result

Causes some test failures
UNFINISHED Implement HTTP POST /restful/rhizome/insert