[Cryptography Team] first cut at CertificateExtensions and ASN1 issues

[Robert Withers]

I made a first cut at parsing the CertificateExtensions.  I grab the  
OID and then I do an ASN1 DER decoding of the value.  We have  
shortcomings in the way we decode the tag for DER/BER encodings.  We  
don't decode multi-byte tags for example.

When I was decoding the cert extensions, I ran across several new  
tags, namely 128 and 130.   According to ASN1dubuisson.pdf, these are  
context-specific, primitive types.  When we have the high order bit  
set, we are masking the low order bits.  I changed the mask to mask  
out the high order bit.  This means that my 2 tags decode to a  
ByteArray, while the ExplicitConstructed type (101xxxxx) still  
decodes correctly.   You may want to review my code in Cryptography- 
ASN package, specifically the ASN1Value class>>#typeClassForTag:

Robert