review request (S): 6981788 GC map generator sometimes picks up the wrong kind of instruction operand

[John Rose]

6981788: GC map generator sometimes picks up the wrong kind of instruction operand
Summary: Distinguish pool indexes from cache indexes in recently changed code.
http://cr.openjdk.java.net/~jrose/6981788/webrev.00

The bug reproduces with ScavengeALot on an invokedynamic instruction and on a fast_aldc instruction (ldc/MH).  

Verified the fix.  Tried it with and without TraceNewOopMapGeneration.

-- John