Accessors should create method for checking element presence

[jkotests]

The standard accessor methods create <name>? to check the existence of an element. In most cases, I would expect people care about the presence (ie exists AND visible).

Ideally, we would change <name>? to check presence. Note that this would be a backwards-incompatible change.

The other option is to add another standard method, but the naming may get confusing.

Originally reported on the Watir-General mailing list: https://groups.google.com/forum/#!msg/watir-general/YapRI27qa3Q/x_lkL1wIEQAJ