Storing timezone-less dates in local time instead of UTC

Issue #225 caused such dates to be read, but not stored in local time.

lib/utils.js

@@ -47,7 +47,7 @@ function arrayString(val) {
 //for complex types, etc...
 var prepareValue = function(val) {
   if(val instanceof Date) {
-    return JSON.stringify(val);
+    return dateToString(val);
   }
   if(typeof val === 'undefined') {
     return null;
@@ -58,6 +58,33 @@ var prepareValue = function(val) {
   return val === null ? null : val.toString();
 };
 
+function dateToString(date) {
+  function pad(number, digits) {
+    number = ""+number;
+    while(number.length < digits)
+      number = "0"+number;
+    return number;
+  }
+
+  var offset = -date.getTimezoneOffset();
+  var ret = pad(date.getFullYear(), 4) + '-'
+    + pad(date.getMonth() + 1, 2) + '-'
+    + pad(date.getDate(), 2) + 'T'
+    + pad(date.getHours(), 2) + ':'
+    + pad(date.getMinutes(), 2) + ':'
+    + pad(date.getSeconds(), 2) + '.'
+    + pad(date.getMilliseconds(), 3);
+
+  if(offset < 0) {
+    ret += "-";
+    offset *= -1;
+  }
+  else
+    ret += "+";
+
+  return ret + pad(Math.floor(offset/60), 2) + ":" + pad(offset%60, 2);
+}
+
 function normalizeQueryConfig (config, values, callback) {
   //can take in strings or config objects
   config = (typeof(config) == 'string') ? { text: config } : config;