.my.cnf generation and parsing.

[geofft]

Per [help.mit.edu #691338], we should replace [mysql] with [client], or depending on compatibility, add a [client] section in addition.

We also have a bug that our parsing of .my.cnf doesn't deal with escaping, so e.g. passwords with # signs aren't escaped, or things that mysql escapes we don't unescape.

[geofft]

[help.mit.edu #781877] reported that replacing the [mysql] heading with a [client] heading seems not to break anything.

[mitchb]

We made the [mysql] -> [client] change long ago. I'm not really sure just how much effort is worth putting into making a php script clever about mysql's config file escaping rules.