boolean argument to toggle functions

[dalangalma]

This is similar to #1681 but more general. I'd like it if all the toggle functions (toggle, toggleClass, slideToggle, etc) could take a boolean to say whether to show or hide them. That way you could replace code that was like:

if (hasErrors) {
  $('#errorPanel).show();
}
else {
  $('#errorPanel).hide();
}

it could just be:

$('#errorPanel').toggle(hasErrors);

[flesler]

This seems like a valid enhancement, I'll take care of this.

[flesler]

Added at [6000] and [6001].