simpler way of checksumming files in a python 2 and 3 compatible way

Author: mamoll

pygccxml/parser/declarations_cache.py

@@ -23,16 +23,9 @@ def file_signature( filename ):
     # - This change allows duplicate autogenerated files to be recognized
     #return os.path.getmtime( source )
     sig = hashlib.md5()
-    try:
-        # try default encoding first
-        f = open(filename, 'r', encoding='utf-8')
-        buf = f.read()
-    except UnicodeDecodeError:
-        # otherwise, try another common encoding
-        f.close()
-        f = open(filename, 'r', encoding='iso8859-1')
-        buf = f.read()
-    sig.update(buf.encode('utf-8'))
+    f = open(filename, 'rb')
+    buf = f.read()
+    sig.update(buf)
     f.close()
     return sig.hexdigest()