patches/ppml: always use base64 encoding for non-utf8 string.

in most cases, where ASCII-range characters are less than 80% of input
non-utf8 string, the result is same but we can reduce needless string
replacement calls. in rare case, for example wrongly iso-8859-1
encoded properties or PDF data, the result becomes different, i.e.
before: ASCII-range characters + escaped characters => after: base64
encoding, but the meaning is still same.

product/ERP5Type/patches/ppml.py

@@ -53,7 +53,7 @@ def convert(S):
         if not isinstance(S, unicode):
             S.decode('utf8')
     except UnicodeDecodeError:
-        new = ''.join([reprs3.get(x) for x in S])
+        return 'base64', base64.encodestring(S)[:-1]
     else:
         new = ''.join([reprs.get(x, x) for x in S])
     ### patch end