autoindex does not escape URIs properly

[Damian Zaremba]

When auto index is enabled on a directory that contains files with 
"special" characters IE "test file.txt" or "funny_file?" it does not 
escape them resulting in in-correctly formed and sometimes completely 
broken links. The expect result being that "test file.txt" is 
transformed into "test%20file.txt" and "funny_file?" transformed into 
"funny_file%3F"

I don't really have a suggestion for fixing it as the code in 
core/ngx_string.c confuses the heck out of me as I'm only a beginner in 
C but I'm sure someone experienced could figure it out quite easily!

Issue appears to exist in 0.8.54 and nginx-0.9.4.

Thanks,
Damian