Added mutalbe copy methods
Add a new constructor that takes a port.

This adds initWithHostName:portNumber:apiPath:customHeaderFields: and
has initWithHostName:apiPath:customHeaderFields: call it in turn.

This allows callers to specify host and port in one step.
Merge pull request #333 from tipbit/init-with-port

Add a new constructor that takes a port.
Fixed a crash when decompressedResponseImage method is called on a network operation that is not a image at all.
Fixed a conflict
Added mutable copy method
Update MKNetworkKit