selectAll and deselectAll can be called on standard select boxes

[chrisnovakovic]

Calling .selectpicker('selectAll') and .selectpicker('deselectAll') on standard (i.e., not multiple) select boxes works, with some consequences that might appear odd to the caller:

• selectAll causes every item in the bootstrap-select box to be highlighted. val() (for both the bootstrap-select and underlying <select>) and the selected item in the bootstrap-select are both the final list item.
• deselectAll doesn't change the highlighting of any items in the bootstrap-select box. val() (for both the bootstrap-select and underlying <select>) is the empty string, and the selected item in the bootstrap-select correctly reverts to the placeholder if there is one.

It doesn't make sense to allow either of these methods to be called on a non-multiple select box, especially given the documentation's implication that they should only be called on multiple select boxes.