[docs] Improve -O docs (issue 17232)

[ezio.melotti at gmail.com]

http://bugs.python.org/review/17232/diff/7583/Doc/using/cmdline.rst
File Doc/using/cmdline.rst (right):

http://bugs.python.org/review/17232/diff/7583/Doc/using/cmdline.rst#newcode214
Doc/using/cmdline.rst:214: :const:`__debug__`.  Change the filename
extension for compiled
Does this link to the place where __debug__ is documented (assuming
there is such place)?

http://bugs.python.org/review/17232/diff/7583/Doc/using/cmdline.rst#newcode221
Doc/using/cmdline.rst:221: Discard docstrings in addition to what
:option:`-O` does.
What about "Like :option:`-O`, but also discard docstrins."?

http://bugs.python.org/review/17232/diff/7583/Modules/main.c
File Modules/main.c (right):

http://bugs.python.org/review/17232/diff/7583/Modules/main.c#newcode69
Modules/main.c:69: -O     : remove assert and __debug__-dependent
statements; change .py\n\
Shouldn't this be .pyc?

http://bugs.python.org/review/17232/diff/7583/Modules/main.c#newcode71
Modules/main.c:71: -OO    : remove doc-strings in addition to the -O
changes\n\
I would re-use the same wording I proposed for the docs.

http://bugs.python.org/review/17232/