Bug#823773: jhighlight: FTBFS: [javadoc] javadoc: error - The -encoding option may be specified no more than once.

[Emmanuel Bourg]

Control: reassign -1 ant
Control: affects -1 jhighlight

This is a bug caused by the patch to make the javadocs reproducible in
ant/1.9.7-1. jhighlight sets the javadoc encoding with an extra argument
(<arg value="-encoding"/>) instead of the 'encoding' attribute of the
javadoc task, and the patch doesn't handle this case.