If we cannot guess the type of local file, fallback to JSON

This is an experimental feature that may need to be reverted
but it seems like it may be a useful hack.

In the past if the type could not be guessed we'd get an
error from the wsgi server. Now, intsead, fallback to application/json.

This makes it possible to drop JSON data files in the assets dir
for local testing. This can be useful when you want to load a tiddler
from local instead of remote. Usually we wouldn't expect these
files to get pushed. In fact the only way I've used it so far
is in a tsapp that _never_ gets pushed.

tsapp/__init__.py

@@ -10,7 +10,7 @@
 import sys
 
 
-__version__ = '0.6.1'
+__version__ = '0.7.0'
 
 
 def error_exit(code, message=""):

tsapp/proxy.py

@@ -242,6 +242,9 @@ def handle_get(environ, start_response, config):
             local_path = path_parts[-1]
             filehandle = in_assets(local_path)
             mime_type = mimetypes.guess_type(local_path)[0]
+            # Fall back to JSON if we cannot guess
+            if not mime_type:
+                mime_type = 'application/json'
         else:
             raise IOError('path wrong length')
         status = '200 OK'