Guard against DOS line endings.

run_tests.py

@@ -93,13 +93,16 @@ def run_tests():
 
 def check_file(fname):
     linenum = 0
-    for line in open(fname).readlines():
-        if '\t' in line:
+    for line in open(fname, 'rb').readlines():
+        if b'\t' in line:
             print("File %s contains a literal tab on line %d. Only spaces are permitted." % (fname, linenum))
             sys.exit(1)
-    linenum += 1
+        if b'\r' in line:
+            print("File %s contains DOS line ending on line %d. Only unix-style line endings are permitted." % (fname, linenum))
+            sys.exit(1)
+        linenum += 1
 
-def check_tabs():
+def check_format():
     for (root, dirs, files) in os.walk('.'):
         for file in files:
             if file.endswith('.py') or file.endswith('.build'):
@@ -110,5 +113,5 @@ if __name__ == '__main__':
     script_dir = os.path.split(__file__)[0]
     if script_dir != '':
         os.chdir(script_dir)
-    check_tabs()
+    check_format()
     run_tests()