If appsecret_proof param is sent in code, do not override in sdk
Improved validation in parseSignedRequest.
Added test cases
Merge pull request #90 from mattynoce/master

If appsecret_proof param is sent in code, do not override in sdk
Merge pull request #104 from gfosco/signedRequest

Improved validation in parseSignedRequest.
fixes #132: Facebook occasionally returns gzip-encoded response