use abspath if path not provided to preserve symlinks

Author: noobCodec

mypy/test/config.py

@@ -6,7 +6,7 @@
 if provided_prefix:
     PREFIX = provided_prefix
 else:
-    this_file_dir = os.path.dirname(os.path.realpath(__file__))
+    this_file_dir = os.path.dirname(os.path.abspath(__file__))
     PREFIX = os.path.dirname(os.path.dirname(this_file_dir))
 
 # Location of test data files such as test case descriptions.