Bug fixes in DiffGenerator.
Changes not compatible with other groovy versions reverted.
WsdlDiffGenerator updated: partDiffGenerator() improved.
Schema updated: getElement() refactored.
Definitions.getElement() refactored.
TypeRefAccessException.java added.
Cycling superType bug fixed.
DiffGenerator for WSDLs with only one PT refactored. Bug fixes.
NullPointer when Schema is null in restriction
Revert "NullPointer when Schema is null in restriction"

This reverts commit 9374163f099357329c935bb60941b4fcabf1c6fc.
#168 Refactored AbstractParserContext so that it becomes responsible on how to cache imported Schema's. This will allow to implement different caching strategies.
Added source jar generation to the pom.
#168 Refactored AbstractParserContext to use the new ParserImportedSchemaCache for caching already parsed schema's. This allows to reuse parsed Schema's for different WSDLs in a multi-threaded environment.
#168 Fixed concurrency issues in the ParserImportedSchemaCache when shared by multiple WSDLParsers
merge