RFR JDK-6321472: Add CRC-32C API

[Staffan Friberg]

Hi,

This RFE adds a CRC-32C class. It implements Checksum so it will have 
the same API CRC-32, but use a different polynomial when calculating the 
CRC checksum.

CRC-32C implementation uses slicing-by-8 to achieve high performance 
when calculating the CRC value.

A part from adding the new class, java.util.zip.CRC32C, I have also 
added two default methods to Checksum. These are methods that were added 
to Adler32 and CRC32 in JDK 8 but before default methods were added, 
which was why they were only added to the implementors and not the 
interface.

Bug: https://bugs.openjdk.java.net/browse/JDK-6321472
Webrev: http://cr.openjdk.java.net/~sfriberg/JDK-6321472/webrev.00

I have started a CCC request for the changes, but was asked to get 
feedback from the core libs group before finalizing the request in case 
there are any API or Javadoc changes suggested.

Thanks,
Staffan