Warn if the Makefile patch hasn't been applied

The old error from the test suite was cryptic.

1 files changed, 11 insertions, 2 deletions

diff --git a/testsuite.py b/testsuite.py
index 906a697..5263720 100644
--- a/testsuite.py
+++ b/testsuite.py
@@ -40,6 +40,7 @@
 
 from __future__ import print_function
 
+import errno
 import kconfiglib
 import os
 import platform
@@ -2433,8 +2434,16 @@ def equal_confs():
     with open(".config") as menu_conf:
         l1 = menu_conf.readlines()
 
-    with open("._config") as my_conf:
-        l2 = my_conf.readlines()
+    try:
+        my_conf = open("._config")
+    except IOError as e:
+        if e.errno != errno.ENOENT:
+            raise
+        print("._config not found. Did you forget to apply the Makefile patch?")
+        return False
+    else:
+        with my_conf:
+            l2 = my_conf.readlines()
 
     # Skip the header generated by 'conf'
     unset_re = r"# CONFIG_(\w+) is not set"