added code in xmlSchemaBuildContentModel to allow ref in group definition

* xmlschemas.c: added code in xmlSchemaBuildContentModel to
  allow ref in group definition (bug 134411).  Also fixed
  misc compilation warning messages.
* result/schema/group0_0_0, result/schema/group0_0_0.err:
  regenerated (now no error reported).
4 files changed