Clean up Tcl/Tk building in the Windows buildbot scripts.

- Nix the 'noxp' option, it was for Win2k compatibility (which was dropped
  with Python 3.3) and made default ttk ugly on post-Win2k systems (#21665)
- Use 'OPTS=symbols' instead of 'DEBUG=1'; symbols is the official method
- Use core, shell, dlls, install-binaries, and install-libraries targets
  instead of all and install to avoid trying to 1) build packages that don't
  work with MSVC 10+ and 2) install unnecessary bits and pieces.
Force a clean pull-and-build of Tcl/Tk on Windows buildbots.
Revert Tools/buildbot/external-common.bat to normal (with updated versions).
Issue #21661: Fix typo.
#21653: fix doc for return type of sqlite3.Row.keys().
#21662: fix typo, improve sentence flow

Patch by Steve Dougherty.