(py-beginning-of-def-or-class, py-end-of-def-or-class,

(py-beginning-of-def-or-class, py-end-of-def-or-class,
py-mark-def-or-class): Integrated Michael Ernst latest patches.
Primarily, it allows functions that search or mark defs/classes based
on programmatic specification, to take an 'either flag value which
allows searching for both classes and defs (stopping at the nearest
construct).

Also clean up some docstrings.