o.c.swt.xygraph: Release elements on CircularBuffer.clear()

Arrays.fill() requires Java 7.
Fixes #727
o.c.swt.xygraph: XYGraph removeTrace() didn't remove from axes

See https://bugs.eclipse.org/bugs/show_bug.cgi?id=445131
Update feature.xml
Update pom.xml
Merge branch 'master' into bug727_circ_buffer_clear

Conflicts:
	applications/features/org.csstudio.scan.ui.feature/feature.xml
	applications/features/org.csstudio.scan.ui.feature/pom.xml
Merge branch 'bug727_circ_buffer_clear'