subclass of source support (makes it nicer for VMs that don't use CPython
bytecode).
+ + chained_path_hook
+ + FileFinder
+
+ - find_module
+
+ + ExtensionFileFinder
+ + PyFileFinder
+ + PyPycFileFinder
+ + PyFileLoader
+
+ - get_code for source only
+ - get_data
+ - source_mtime
+ - source_path
+
+ + PyPycFileLoader(PyFileLoader)
+
+ - get_code
+ - bytecode_path
+ - write_bytecode
+
* Implement PEP 302 protocol for loaders (should just be a matter of testing).
+ Source/bytecode.