for review (M): 6863023: need non-perm oops in code cache for JSR 292

[John Rose]

I have sufficient reviews for 6863023 as of webrev.03, but the GC  
interactions are (sigh) more subtle than I anticipated, and I want to  
get it right.

Here is a fresh layer of changes, required to ensure that strong-root  
nmethods get scavenged exactly once.
   http://cr.openjdk.java.net/~jrose/6863023/diff-02-to-03 (these  
specific changes)
   http://cr.openjdk.java.net/~jrose/6863023/webrev.03 (full webrev)

These changes fix some double-tracing bugs, but they are not correct.   
However, they are not right yet.  What I'm asking for now is (a)  
further advice for structuring the nmethod-walking code correctly, and  
(b) help spotting bugs.

-- John