RFR (S) Make tenuring threshold unsigned

[Jesper Wilhelmsson]

Hi,

While working on a different change I noticed that the tenuring threshold was 
stored in a signed int. This struck me as odd, and since I wanted to avoid 
some unintuitive casts in my other change I would prefer to change the 
threshold to an unsigned.

The change is available here:

http://cr.openjdk.java.net/~jwilhelm/TenuringThreshold/

Several files are touched but there's just type changes in a few places per file.

In this change I also change the declared type of -XX:MaxTenuringThreshold and 
-XX:InitialTenuringThreshold to uintx. This should not be a problem since we 
don't allow negative values for these flags anyway.
/Jesper