AbstractTransform should not catch transformers exceptions

AbstractTransform should not catch transformer exception but throw them instead.

This would allow the caller to handle it correctly and help the developers find which file attachment name in which Nuxeo document has triggered the problem.

The AbstractTransform is indeed two deep in the call stack and has no idea of the Nuxeo document being transform and therefore cannot log all necessary data to make debugging easy.

Fixing this problem requires an API change: add new throws declaration on the method:

public List<TransformDocument> transform(
Map<String, Map<String, Serializable>> options,
TransformDocument... sources);

Therefore this change cannot be implemented in the 5.1 branch.