RFR 8071627: Code refactoring to override == operator of Symbol*

[Calvin Cheung]

Please review this enhancement for Symbol comparison.
This should allow future enhancement such as multiple SymbolTable and 
symbols with the same utf8 strings in different tables should be 
considered "equivalent".

Although this changeset touches many files, the main change is in 
src/share/vm/oops/symbol.hpp with a new SymbolRef class. The rest of the 
change is mostly replacing Symbol* with SymbolRef.

Since currently there's only one single SymbolTable, it isn't feasible 
to write a specific testcase for this enhancement. We will provide a 
testcase when this enhancement is used.

Note also that the copyright header will be fixed before this changeset 
is committed.

JBS: https://bugs.openjdk.java.net/browse/JDK-8071627

webrev: http://cr.openjdk.java.net/~ccheung/8071627/webrev.00/

Tests:
     JPRT
     nsk.jvmti on linux_x64

     the following performance benmarks on linux_x64, solaris_x64, 
solaris_sparc, mac, windows_x64 with no significant performance 
degradation:
         jetstream, scimark, specjbb2000, specjbb2005, specjvm98, volano25

     some internal class loading performance tests

thanks,
Calvin