The JavaAgent lives in ij1-patcher.jar now, not in ij-legacy.jar

It moved quite a while ago; Therefore should suggest to use
ij1-patcher.jar as Java agent instead.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #15 from imagej/java-agent

The JavaAgent lives in ij1-patcher.jar now, not in ij-legacy.jar