Eclipse IDE: Automatically remove trailing whitespace on save

Our project coding conventions do not want trailing whitespace at
the end of a source code line.  Configure Eclipse to automatically
remove them when saving any Java source file.

Change-Id: I9701366b3b1240879761b30556e6ff416e969e1d
Reviewed-by: Mykola Nikishov <mn@mn.com.ua>
Reviewed-by: Alex Blewitt <alex.blewitt@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>