<i18n dev> RFF : 7196533 : TimeZone.getDefault() slow due to synchronization bottleneck

[Seán Coffey]

Recent changes in java.util.TimeZone created new setter and getter 
methods for setting and obtaining the defaultTimeZone for VM.

Synchronization on these methods has caused some performance issues for 
VMs making heavy usage of TimeZone.getDefault()

Fix is to remove synchronization and make the mainAppContextDefault 
variable volatile.

webrev : http://cr.openjdk.java.net/~coffeys/webrev.7196533.jdk8/ 
<http://cr.openjdk.java.net/%7Ecoffeys/webrev.7196533.jdk8/>
bug report : http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7196533

regards,
Sean.