8019380: doclint warnings in java.nio.**

[Alan Bateman]

This is another installation of javadoc fixes reported by doclint. The 
changes are trivial and fix all remaining html and accessibility issues 
in java.nio, java.nio.channels.** and java.nio.file.**. I've also fixed 
the missing @return/@param issues in java.nio.charset but there is 
further work required there to sort out the remaining accessibility 
issues. The webrev with the patch is here:

http://cr.openjdk.java.net/~alanb/8019380/webrev/

Note that there is one change to java.sql.SQLInput, this is to docs 
warnings that slipped in with the javadoc fixes in the JDBC classes.

-Alan.