Crash fix for a case where the EndCallback is not set and used

Change-Id: I49230ac6971a8f65e6ce32d0050e4294baf6c7f2
potential fix for selector exception in L preview.

https://github.com/koush/AndroidAsync/issues/196

Change-Id: Ied509b8704f26fa9ec9efa81672ab918436239d5
use another hash function if MD5 is not available

Change-Id: Ib1117ec589300d6398714bb333c9eb22aa1b7609
Fix a rare NPE crash in Android 2.x
See http://crashes.to/s/5ee30776a5d

Change-Id: I28fbd3552fc057a4ece096d478e20bb83346af8f