Fix a few digest authentication issues

Resolves: #181

lib/api-functions.coffee

@@ -82,7 +82,7 @@ udpConReq = (address, un, key, callback) ->
 httpConReq = (url, username, password, timeout, callback) ->
   options = URL.parse(url)
   # Ensure socket is reused in case of digest authentication
-  agent = new http.Agent({maxSockets : 1})
+  options.agent = new http.Agent({maxSockets : 1})
 
   statusToError = (statusCode) ->
     switch statusCode

lib/auth.coffee

@@ -72,9 +72,7 @@ exports.digest = (username, password, uri, httpMethod, body, authHeader) ->
   authString += ",nonce=\"#{authHeader.nonce}\""
   authString += ",uri=\"#{uri}\""
   authString += ",algorithm=#{authHeader.algorithm}" if authHeader.algorithm?
-  authString += ",qop=#{qop}"
-  authString += ",nc=#{nc}"
-  authString += ",cnonce=\"#{cnonce}\""
+  authString += ",qop=#{qop},nc=#{nc},cnonce=\"#{cnonce}\"" if qop?
   authString += ",response=\"#{response}\""
-  authString += ",opaque=\"#{authHeader.opaque}\""
+  authString += ",opaque=\"#{authHeader.opaque}\"" if authHeader.opaque?
   return authString