Fixed A Few Pong Issues

* Since we're saving phone numbers as 'numeric' in the database we need to remove non-numeric characters before comparing any phone numbers
* We're also using strrpos to compare 'sender', 'from' because some people might use '000-000-0000' in their sms config vs '+10000000000'. Both work.
Fix

* The ping query will always return a $ping[0]['ping_id']. It will be NULL if nothings found.
Merge pull request #51 from ushahidi/pongs-2

Fixes to Receiving SMS Replies