Prefer the locally installed version of AVA.

This hunts for AVA in the locally installed project, and runs that
CLI instead of the globally installed one.

Fixes avajs#157.

cli.js

@@ -1,6 +1,19 @@
 #!/usr/bin/env node
 'use strict';
 
+// Prefer the local installation of AVA.
+var resolveFrom = require('resolve-from');
+var localCLI;
+try {
+	localCLI = resolveFrom('.', 'ava/cli');
+} catch (e) {}
+
+if (localCLI && localCLI !== __filename) {
+	console.warn('Using local install of AVA.');
+	require(localCLI);
+	return;
+}
+
 var debug = require('debug')('ava');
 
 if (debug.enabled) {

package.json

@@ -128,5 +128,8 @@
         "test[/\\\\]"
       ]
     }
+  },
+  "xo": {
+    "ignore": ["cli.js"]
   }
 }

readme.md

@@ -116,6 +116,9 @@ $ ava --help
 
 Files starting with `_` are ignored. This can be useful for having helpers in the same directory as your test files.
 
+*WARNING: NON-STANDARD BEHAVIOR:* The AVA CLI will always try to find and use your projects local install of AVA.
+ This is true even when you run the global `ava` command. This non-standard behavior solves an important [issue](https://github.com/sindresorhus/ava/issues/157),
+ and should have no impact on everyday use.
 
 ## Documentation