Don't subclass ThreadLocal.
Don't subclass ThreadLocal.

This attempts to address issue 402, wherein subclassing ThreadLocal is pinning a reference to a class, which transitively pins the entire application in containers like Tomcat.

git-svn-id: 7b8be7b2f8bf58e8147c910303b95fa2b8d9948f@1214 2534bb62-2c4b-0410-85e8-b5006b95c4ae

byterom/android_external_gson,Mahdi-Rom/android_external_gson,ThirdProject/android_external_gson,CyanogenMod/android_external_gson,TEAM-Gummy/android_external_gson