7127687: MethodType leaks memory due to interning

[John Rose]

http://cr.openjdk.java.net/~jrose/7127687/webrev.00/

7127687: MethodType leaks memory due to interning
Summary: Replace internTable with a weak-reference version.

This is a point fix for JDK 8, and will (pending approval) also be back-ported to JDK 7u.

— John

Notes on process:  This code is part of JSR 292.  Therefore the review comments will be collected in mlvm-dev, and changes will be integrated via hsx/hotspot-comp.

At least one reviewer must be an official Reviewer the JDK 8 Project [1], but other reviewers are most welcome.

[1] http://openjdk.java.net/census#jdk8