The obvious solution here would require that the lazy-loaded tree code always pre-load one additional level of the tree hierarchy when expanding a branch node so that each child of the branch can be determined to be either another branch node (display +/- controls) or a leaf node (no +/- controls).

This may cause some undesirable performance degradation on very large-data sets, so we should make this an optional behaviour, configurable via a new value for the existing "expansionMode" attribute: org.icefaces.ace.component.tree.TreeExpansionMode.extServer (extended server).

r46279: fix to check if a node is a leaf node in lazy mode, only if the immediate parent is expanded

I verified that, in lazy mode, child nodes are only being loaded if the current node is expanded, as intended.

This fix checks its immediate parent to see if its state is expanded. If so, we allow the code to go ahead and check if the current node is a leaf node (by loading its children), and thus we can determine whether to load the expansion/contraction icons or nothing at all.

r46280: committed fix to the 3.3 EE maintenance branch

Verified IF4 trunk r46287/ EE-3.3.0-maintenance branch r46288 in IE8/9/10/11, FF41, Chrome46.
Two random IndexOutOfBoundsExceptions have been seen while testing on the maintenance branch, however these errors could not be reproduced again.