New member variable "index" on Position (used for first/last checks).

New member variable "index" on Position (used for first/last checks).
Position numbering implemented in BlockStackingLayoutManager (see member variables: lastGeneratedPosition and smallestPosNumberChecked)
Use notifyPos to give a Position an index (Don't reuse Position instances that get an index!)
Flags on TableContentPosition indicating first and last status (see TableStepper).
New way of determining first/last area implemented on all currently implemented block-level FOs.
Removed obsolete isBogus() method from LayoutManager.
Removed duplicate wrapPositionElements() method in FlowLayoutManager.
Some javadocs here and there.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@198701 13f79535-47bb-0310-9956-ffa450edef68