[CXF-5254] Unmarshall exception if a sequence<string> is used in a struct

Here's an attempt to resolve this issue. The main problem is with sequence handling:
* IDL 2 WSDL+CorbaBinding: always produces *wrappers* for sequences
* WSDL 2 WSDL+CorbaBinding: there may be elements nested inside ComplexType which have `minOccurs!=1` or `maxOccurs!=1` - these are *unwrapped* sequences

at runtime, when writing XML events to CorbaStreamWriter and while reading XML events from CorbaStreamReader there should be proper handling of sequence *wrappers*.

Here's a patch with all necessary test cases.

regards
Grzegorz Grzybek