Update watched file list when files are added or removed (#1539)

Currently we build the Sass import graph when the CLI watcher is
started. However the graph is not update updated when files are
added or deleted. The latest is a big deal but the former results
in new files not triggered rebuilds when they're changed. The only
way to currently resolve this is to restart the CLI watcher.

This patch rebuilds the Sass import graph when files are added or
deleted to the watch always works as expected.

Fixes #1538

bin/node-sass

@@ -230,16 +230,24 @@ function getOptions(args, options) {
  */
 
 function watch(options, emitter) {
-  var watch = [];
+  var buildGraph = function(options) {
+    var graphOptions = {
+      loadPaths: options.includePath,
+      extensions: ['scss', 'sass', 'css']
+    };
+
+    if (options.directory) {
+      var graph = grapher.parseDir(options.directory, graphOptions);
+    } else {
+      var graph = grapher.parseFile(options.src, graphOptions);
+    }
 
-  var graphOptions = { loadPaths: options.includePath, extensions: ['scss', 'sass', 'css'] };
-  var graph;
-  if (options.directory) {
-    graph = grapher.parseDir(options.directory, graphOptions);
-  } else {
-    graph = grapher.parseFile(options.src, graphOptions);
+    return graph;
   }
 
+  var watch = [];
+  var graph = buildGraph(options);
+
   // Add all files to watch list
   for (var i in graph.index) {
     watch.push(i);
@@ -260,6 +268,14 @@ function watch(options, emitter) {
       }
     });
   });
+
+  gaze.on('added', function(file) {
+    graph = buildGraph(options);
+  });
+
+  gaze.on('deleted', function(file) {
+    graph = buildGraph(options);
+  });
 }
 
 /**