[7u4] Request for approval for CR: 7142086 performance problem in Check.checkOverrideClashes(...)

[Jim Holmlund]

Request for Backport of a JDK 8 fix into 7u4.

Bug description  :     
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7142086


The fix  is the same as in JDK 8:
   JDK 8 changeset :   
http://hg.openjdk.java.net/jdk8/tl/langtools/rev/84b61130cbed

The fix has passed the JDK 8 nightly build and tests, and jdk-7u langtools regression and 
jck-compiler tests

jjh