Added becommands/commit.py and minor fixes.

Added becommands/commit.py and minor fixes.

Now we can commit changes from the command line with a unified
interface.  The interface is much less flexible than using your
particular version control system's commit command directly, so this
command is mostly intended for user-interfaces and other tools that
don't want to be bothered with the extra flexibility.

Normalized spacing in rcs.RCS.commit to produce:
  summary
  <BLANKLINE>
  body
  <TRAILING-ENDLINE>
messages regardless of the input string format.

Also fixed a "--complete" handline bug in cmdutil, and some minor
docstring typos in libbe.rcs and .editor.