Fix improper use of NSLocalizedDescriptionKey.

This commit fixes a typo where an underlying error (NSError object) was associated with NSLocalizedDescriptionKey that is expected to be NSString.
Changed delegates from unsafe_unretained to weak
Removed nill-checks
introduce closed flag to XHR transport. fix #130.
Merge commit '7f21f85633bfbe1867a47d2c6528f0bcd7af573d' into develop

# By Menno Pruijssers
# Via Menno Pruijssers
* commit '7f21f85633bfbe1867a47d2c6528f0bcd7af573d':
  Removed nill-checks
  Changed delegates from unsafe_unretained to weak

Conflicts:
	SocketIOTransportXHR.h
Instantiate errorInfo NSMutableDictionary using mutableCopy as suggested by Elshad. close #125.
fix unix timecode bug in handshake url. close #118.
Merge commit '82459870e6f00fbe666a88ee279ee0c553345d95' into develop. close #126.

# By Sergei
# Via Sergei
* commit '82459870e6f00fbe666a88ee279ee0c553345d95':
  Fix improper use of NSLocalizedDescriptionKey.

Conflicts:
	SocketIO.m
bump to version 0.4.1
v0.4.1

# By Menno Pruijssers (2) and others
  fix unix timecode bug in handshake url. close #118.
  Instantiate errorInfo NSMutableDictionary using mutableCopy as suggested by Elshad. close #125.
  introduce closed flag to XHR transport. fix #130.
  Removed nill-checks
  Changed delegates from unsafe_unretained to weak
  Fix improper use of NSLocalizedDescriptionKey.