7197637: (ch) sun.nio.ch.Default* cause providers for other platforms to be included in rt.jar

[Alan Bateman]

sun.nio.ch.DefaultSelectorProvider and 
DefaultAsycnhronousChannelProvider select the appropriate provider based 
on the OS. As there are static references to each of the provider 
classes it means the classes for other platforms get compiled implicitly 
and so there are additional classes in rt.jar that are never used. The 
real issue here is that we don't separate Solaris and Linux specific 
code and this is something that I think that we will need to addressed 
some day. In the mean-time I've changed the create methods to use 
reflection, in the same way that we already have in 
sun.nio.fs.DefaultFileSystemProvider.

Mandy - while I was there I also changed the class loader specified to 
Class.forName to be the defining loader of the Default* class, this 
change has no effect for now but may avoid us needing to change this 
again when we eventually move to modules.

The webrev with the proposed changes is here:

http://cr.openjdk.java.net/~alanb/7197637/webrev/

-Alan.