Namespace autoloaded functions (#1724)

Since functions defined in files referenced in 'files' section in
composer autoload config are automatically loaded when composer
autoloader is included (for example when Psalm is installed into project
vendors), it's good idea to keep them namespaced. Otherwise it would
prevent dependents to declare their own functions in the global
namespace with the same names.

src/Psalm/Config.php

@@ -21,8 +21,6 @@ use Psalm\Progress\Progress;
 use Psalm\Progress\VoidProgress;
 use SimpleXMLElement;
 
-use function isAbsolutePath;
-
 class Config
 {
     const DEFAULT_FILE_NAME = 'psalm.xml';

src/functions.php

@@ -1,4 +1,8 @@
 <?php
+namespace Psalm;
+
+use InvalidArgumentException;
+
 /**
  * @param string $path
  *

tests/IsAbsolutePathTest.php

@@ -1,6 +1,8 @@
 <?php
 namespace Psalm\Tests;
 
+use function Psalm\isAbsolutePath;
+
 class IsAbsolutePathTest extends TestCase
 {
     /**