Fix katiefenn#30.

This uses https://www.npmjs.org/package/graceful-fs as a drop-in
replacement for the fs module. This will of course have a minor
performance impact, but it should make Parker more resilient when
processing large numbers of stylesheets.

See also:
http://stackoverflow.com/a/15934766/349353
nodejs/node-v0.x-archive#5401 (comment)

package.json

@@ -8,7 +8,8 @@
         "underscore": "*",
         "cli-color": "*",
         "minimist": "0.0.7",
-        "async": "~0.2.10"
+        "async": "~0.2.10",
+        "graceful-fs": "~3.0.2"
     },
     "devDependencies": {
         "chai": "*",

parker.js

@@ -14,7 +14,7 @@ var _ = require('underscore'),
     metrics = require('./metrics/All'),
     formatters = require('./lib/Formatters'),
     argv = require('minimist')(process.argv.slice(2)),
-    fs = require('fs'),
+    fs = require('graceful-fs'),
     async = require('async'),
     path = require('path'),
     info = require('./lib/Info');