Patch version 3:
 - update posix documentation
 - improve os.environ and os.getenv() documentation: specify the type and document the encoding/error handler, add a link to environb/getenvb
 - os.environ and os.environb now check the argument types (raise a better error), on Windows and Unix. Before my patch, os.environ[b'key']=b'value' sets the variable "b'key'" to "b'value'" :-(
 - restore os.environb in TestEnviron.tearDown() (test_os)
 - fix patch on posixmodule.c indentation
 - fix a regression introduced by my patch: set PyErr_NoMemory() on error  (newstr==NULL in posixmodule.c)
 - rename keymap to encodekey