Support dr_delete_fragment for shared cache

Currently, dr_delete_fragment() is only supported for thread private caches.

This issue relates to adding support for dr_delete_fragment() to shared caches.

Initial information can be found in the user-group [here](https://groups.google.com/forum/#!topic/DynamoRIO-Users/IEoeF8EpTz4). I am now migrating updates to Github as they are more technical in relation to DR's internals.