8154077: (fs) Reduce number of file system classes loaded during startup

[Alan Bateman]

With jimage using the file system and channel APIs then there are more 
NIO classes loaded during startup that previously. Brian Burkhalter and 
I chatted briefly about it and there are a number of things that we can 
do. The following is a first installation to improve 
isRegularFile/isDirectory/exists for the common "no options" cases:

   http://cr.openjdk.java.net/~alanb/8154077/webrev/

This is the Unix provider only for now, we need to follow-up on with 
some Windows specific changes but this can be done independently.

-Alan