Request for reviews (L): 6939207: refactor constant pool index processing

[John Rose]

I made slight updates to the assertion-checking code, and added a missing "__ ldx" to the SPARC code.  (It is obvious in retrospect.)

This updated webrev is probably final:
  http://cr.openjdk.java.net/~jrose/6939207/webrev.04/

New diffs:
  http://cr.openjdk.java.net/~jrose/6939207/webrev.04/diff-03-to-04.patch

-- John