JavaxScriptRunner:
- Better compiled script reference name to avoid reference name
  collision, project wide : execName + ".compiled." +
  getScript().hashCode() + "." + getProject().hashCode();

ScriptDef:
- Fixed Javadoc + use of 3rd person
  [(oracle style
guideline)](http://www.oracle.com/technetwork/articles/java/index-137868.html#styleguide)

Task manual: documentation for `encoding` and `compiled` options.
- `encoding` : script.html, scriptdef.html, conditions.html,
   selectors.html, mapper.html, filterchain.html
- `compiled` : scriptdef.html

Added source file `encoding` option on:
- org.apache.tools.ant.taskdefs.optional.Script
- org.apache.tools.ant.types.optional.AbstractScriptComponent
  (inherited by ScriptCondition, ScriptMapper)
- org.apache.tools.ant.types.optional.ScriptFilter
- org.apache.tools.ant.types.optional.ScriptSelector

Test units :
- org.apache.tools.ant.taskdefs.optional.script.ScriptDefTest,
  script.xml : src + encoding
- org.apache.tools.ant.taskdefs.optional.RhinoScriptDefTest,
  scriptdef.xml : src + encoding, compiled
- new file: src/etc/testcases/taskdefs/optional/script/heavy-script.js