[RFA] Fix "set" handling of Python parameters

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:

Tom> It's long bothered me that setting a Python parameter from the CLI
Tom> will print the "set" help text by default.  I think usually "set"
Tom> commands should be silent.  And, while you can modify this behavior a
Tom> bit by providing a "get_set_string" method, if this method returns an
Tom> empty string, a blank line will be printed.

Tom> This patch removes the "help" behavior and changes the get_set_string
Tom> behavior to avoid printing a blank line.  The code has a comment about
Tom> preserving API behavior, but I don't think this is truly important;
Tom> and in any case the workaround -- implementing get_set_string -- is
Tom> trivial.

Tom> Regression tested on x86-64 Fedora 26.

Ping.

Tom