use another hash function if MD5 is not available
Fix a rare NPE crash in Android 2.x
See http://crashes.to/s/5ee30776a5d
Merge pull request #216 from robUx4/npe_android2x

Fix a rare NPE crash in Android 2.x
Merge pull request #215 from robUx4/missing_md5_workaround

use another hash function if MD5 is not available
Merge branch 'master' of https://github.com/koush/AndroidAsync

# By Steve Lhomme
# Via Koushik Dutta (2) and Steve Lhomme (1)
* 'master' of https://github.com/koush/AndroidAsync:
  Fix a rare NPE crash in Android 2.x See http://crashes.to/s/5ee30776a5d
  use another hash function if MD5 is not available