ECLIPSE_LAUNCHER might contain multiple lines: use the most recent one

After upgrading to Eclipse 4.4, I've ended up with:

> find /opt/eclipse/plugins -name 'org.eclipse.equinox.launcher_*.jar'
  /opt/eclipse/plugins/org.eclipse.equinox.launcher_1.3.0.v20140415-2008.jar
  /opt/eclipse/plugins/org.eclipse.equinox.launcher_1.3.0.v20130327-1440.jar

This results in "Unable to locate the eclipse launcher jar.", because
the `test -e` fails.