[7u6] Request for Approval of 7175758 : Improvements to Collisions.java regression test

[Mike Duigou]

This is a fix for a regression test to include cases uncovered by a recently fixed bug CR#7174736. The patch is currently under review for JDK8 at http://cr.openjdk.java.net/~mduigou/7175758/0/webrev/ . This request is being made before the changeset is committed to jdk 8 in order to meet tomorrow's rampdown deadline. 

The code changes for jdk7u6 are identical to the ones in jdk8.

When approved and committed for JDK 8 I intend to push it to
   ssh://hg.openjdk.java.net/jdk7u/jdk7u-dev-gate/jdk

Regards,

Mike