use os.tmpdir() polyfill for more consistent behaviour

lib/tmp.js

@@ -16,7 +16,7 @@ var
   crypto = require('crypto'),
   exists = fs.exists || path.exists,
   existsSync = fs.existsSync || path.existsSync,
-  tmpDir = os.tmpDir || _getTMPDir,
+  tmpDir = require('os-tmpdir'),
   _c     = require('constants');
 
 
@@ -72,25 +72,6 @@ function _randomChars(howMany) {
   return value.join('');
 }
 
-/**
- * Gets the temp directory.
- *
- * @return {String}
- * @api private
- */
-function _getTMPDir() {
-  var tmpNames = ['TMPDIR', 'TMP', 'TEMP'];
-
-  for (var i = 0, length = tmpNames.length; i < length; i++) {
-    if (_isUndefined(process.env[tmpNames[i]])) continue;
-
-    return process.env[tmpNames[i]];
-  }
-
-  // fallback to the default
-  return '/tmp';
-}
-
 /**
  * Checks whether the `obj` parameter is defined or not.
  *

package.json

@@ -33,7 +33,9 @@
     "node": ">=0.4.0"
   },
 
-  "dependencies": {},
+  "dependencies": {
+    "os-tmpdir": "~1.0.0"
+  },
 
   "devDependencies": {
     "vows": "~0.7.0"