Improve man pages in `scripts' directory.

Improve man pages in `scripts' directory.

help2man is quite picky:

  . It needs newlines to properly identify the various sections.

  . Examples must start with a shell prompt character.

  . Multiple usage lines needs the same indentation.

  . I've replaced the `Bugs' string with an empty one in the call
    to the `addoption_group' since it confuses help2man otherwise.

Note that man page output is still not optimal yet; some constructs
can't be handled well by automatic parsing.