PSR4: prevent user-defined namespace overriding vendored

Fixes #22 (closed)

Test failed because of changed array keys. Not sure how bad that is:

There was 1 failure:
1) TestApp1\PSR4Test::testGetClassesInNamespaceRecursively with data set #2 ('TestApp1\Multi', array('TestApp1\Multi\Uij', 'TestApp1\Multi\Yij', 'TestApp1\Multi\Uik', 'TestApp1\Multi\Yik', 'TestApp1\Multi\Yop\Rik', 'TestApp1\Multi\Yop\Tik', 'TestApp1\Multi\Yop\Eij', 'TestApp1\Multi\Yop\Rij'), 'ClassFinder should be able to...ot"] )')
ClassFinder should be able to find 1st party classes recursively when a provided namespace root maps to multiple directories (Example: "HaydenPierce\SandboxAppMulti\": ["multi/Bop", "multi/Bot"] )
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
     1 => 'TestApp1\Multi\Yij'
     2 => 'TestApp1\Multi\Uik'
     3 => 'TestApp1\Multi\Yik'
-    4 => 'TestApp1\Multi\Yop\Rik'
-    5 => 'TestApp1\Multi\Yop\Tik'
-    6 => 'TestApp1\Multi\Yop\Eij'
-    7 => 'TestApp1\Multi\Yop\Rij'
+    8 => 'TestApp1\Multi\Yop\Rik'
+    9 => 'TestApp1\Multi\Yop\Tik'
+    10 => 'TestApp1\Multi\Yop\Eij'
+    11 => 'TestApp1\Multi\Yop\Rij'
 )