Returns <code>true</code> if the receiver can navigate to the
previous session history item, and <code>false</code> otherwise.
@return the receiver's back command enabled state
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Returns <code>true</code> if the receiver can navigate to the previous session history item, and <code>false</code> otherwise.
@return the receiver's back command enabled state
@exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>
@see #back