new fallbackmimetype argument to guess_mimetype and encoding

__init__.py

@@ -70,7 +70,8 @@ def guess_encoding(buffer, fallbackencoding=None):
     return fallbackencoding or DEFAULT_ENCODING
 
 def guess_mimetype_and_encoding(format=None, encoding=None, data=None,
-                                filename=None, fallbackencoding=None):
+                                filename=None, fallbackencoding=None,
+                                fallbackmimetype=u'application/octet-stream'):
     if format and format.split('/')[-1] in BINARY_ENCODINGS:
         format = None # try to do better
     if filename and not format:
@@ -81,7 +82,7 @@ def guess_mimetype_and_encoding(format=None, encoding=None, data=None,
         elif enc:
             format = u'application/%s' % enc
         else:
-            format = u'application/octet-stream'
+            format = fallbackmimetype
     if not encoding and data and format and is_text_mimetype(format):
         encoding = guess_encoding(data, fallbackencoding)
     return format, encoding