check HTTP status code of NSURLConnection responses during xhr polling transport just like when checking HTTP status code during handshake. Handles case when server restarts while connection with device is already established.
clean code
Merge commit '9e03bceb0df9e4ee20f787e3c01897b53b515e30' into develop
v0.5.2

-  check HTTP status code of NSURLConnection responses during xhr polling transport
update changelog to v0.5.2
Merge commit 'c7e5d27b135d31e4ce81f066176b1719659c0e14' into develop-hs