more work concerning navigation within BTextView:
* pressing HOME on last line works again
* made public versions of LineAt() do what is required to pass back the
correct value even for the last line of the buffer (original implementation
has been moved to private _LineAt())
* PAGE_UP/PAGE_DOWN now moves the view by the bounds-height, making the
behaviour somewhat less confusing (IMHO, please shout if that's not
acceptable for you)
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@30459 a95241bf-73f2-0310-859d-f6bbb57e9c96