try harder to read files with right encoding

Author: mamoll

pygccxml/parser/declarations_cache.py

@@ -23,8 +23,16 @@ def file_signature( filename ):
     # - This change allows duplicate autogenerated files to be recognized
     #return os.path.getmtime( source )
     sig = hashlib.md5()
-    f = open(filename,'r')
-    sig.update(f.read().encode('utf-8'))
+    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.close()
     return sig.hexdigest()