Fixed hashCode() method that returned inconsistent value.

Other changes:

  * DataFlow: Added javadoc comment which describes the meaning of
    an empty action list.
  * Fixed typo in javadoc comment.

Change-Id: I7c0e31b463ce62bcdb3918266fdb1a8988c699d6
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>
Merge "Fixed hashCode() method that returned inconsistent value."