Ensure constant time random access in ElemNameSeqReader.

[omatzcoveo]

Hi there,

Parsing large sequences has performance issues : I traced it back to a quadratic behavior in a loop using ElemNameSeqReader.

ElemNameSeqReader's use of isDefinedAt presuppose constant time random access in its internal seq, but it ends up doing it on a List, I believe fed from AnyElemNameParser. This diff both builds a Vector instead of a List from AnyElemNameParser, and enforces a Vector in ElemNameSeqReader internals. This is successful in fixing the performance issue we've observed at my company.

Let me know if you need me to do something else in the pull request (do I have to do something special to update src_managed/scalaxb/scalaxb.scala ?).

Thanks

[eed3si9n]

@omatzcoveo Thanks for the contribution. Could you fix the failing integration tests please?

[omatzcoveo]

Last friday I opted to reduce the scope of the change in order not to have any impact on tests and such, and only keep the important bit that removes the quadratic behavior. Thanks!

[eed3si9n]

Nicely done.