Updates to support SunJCE provider

[Berin Lautenbach]

Well the whole thing about supporting the SunJCE provider turned out to 
be a bit harder than expected.

To cut a long story short - the reason the SHA1WithRSA signatures were 
failing under the beta of JDK 1.5 is that the class name of the 
SunRsaSign provider has changed.  So I've added a second Provider 
descriptor for SunRsaSign in config.xml and updated the JCEMapper class 
to run through multiple descriptors for providers of a given Id when 
trying to determine whether the particular provider is loaded.

I've also updated the encryption unit tests so that they now test for 
the presence of ISO padding and Key Wrap algorithms.  If these are not 
available, the unit tests will skip the relevant tests and output a warning.

So the unit tests will now pass for BC, JDK 1.4 and JDK 1.5 providers.

Note that all the signature tests pass for all three cases.

Cheers,
        Berin