Improve coding cookie regex based on Serhiy's advice, with new test.

Author: Guido van Rossum

mypy/test/data/parse-errors.test

@@ -481,6 +481,14 @@ file:2: error: Unknown encoding 'uft8'
 [out]
 file:4: error: Unrecognized character
 
+[case testDoubleEncoding4]
+
+
+# coding: ascii
+á = 1
+[out]
+file:4: error: Unrecognized character
+
 [case testLongLiteralInPython3]
 2L
 0x2L

mypy/util.py

@@ -7,7 +7,7 @@
 
 T = TypeVar('T')
 
-ENCODING_RE = re.compile(br'(\s*#.*(\r\n?|\n)){0,1}?\s*#.*coding[:=]\s*([-\w.]+)')
+ENCODING_RE = re.compile(br'([ \t\v]*#.*(\r\n?|\n))??[ \t\v]*#.*coding[:=][ \t]*([-\w.]+)')
 
 default_python2_interpreter = ['python2', 'python', '/usr/bin/python']