Require Java SE 7

Fork-join framework is in Java SE 7. So have deleted source for
jsr166y, which required access to restricted apis.
Update scripts for Java SE 7.
Update build for Scala 2.10

Scala builds (enabled if SCALA_HOME is set) now require
scala-reflect.jar.
Cleanup

No substantive changes.
Cleanup
Cleanup.
Cannot use @link in scaladocs.
New build system; now using Gradle instead of Apache Ant.

Note that directory names have been changed to better conform to
conventions of Gradle (and Maven). Changes may be required for scripts
that set the classpath.
Updated scripts to run java and jython programs.

Changed directory name jar to libs, to conform to Gradle build
conventions.
Document the switch to Gradle.
 Merge remote-tracking branch 'upstream/master'