Catch Ceylon assertion errors coming from the ceylon module, so it will
only disable the use of structural-aware incremental build, but will not
stop the build with an exception.
Check if the delta is null.
Also visit module descriptors during incremental build
Now use the model delta to avoid doing full build when a modified
package or module descriptor is struturally unchanged (only comments,
spaces or some annotations like license, by, etc ... were changed).