[PATCH 0 of 7] try_files fixes

[Maxim Dounin]

Hello!

The following patch series addresses multiple issues as observed with
the "try_files" directive, notably when used with "alias" or when
requests are proxied after "try_files".  Changes include:

- Both variables and static strings in "try_files" arguments are now
  handled consistently and expected to be in URI space, matching the
  documentation.  Previously, static strings in prefix locations with
  alias were interpreted as an addition to alias.  With this change,
  configuration like this:

    location /prefix/ {
        alias /foo/;
        try_files /prefix/bar =404;
    }

  will actually try the "/foo/bar" file, and not "/foo/prefix/bar",
  matching what "try_files $uri" does with a request to "/prefix/bar".

- In regex locations with alias, "try_files $uri ..." is now properly
  supported.  Previously, only adding extensions worked in such
  locations, as in "try_files .html ...".  Also, using try_files in such
  locations now produces correct URI.

- Proxying with URI replacement after try_files now aware if URI was
  modified by try_files, and the following configuration will not corrupt
  URI in requests to backend (or segfault, if URI is shorter than the
  location prefix), but rather will avoid URI replacement (similarly to
  what happens after rewrites):

    location /prefix/ {
        try_files /prefix.../test =404;
        proxy_pass http://backend/remote/;
    }

- Proxying after try_files now uses URI modified by try_files even if
  original unparsed URI is still available, so the following configuration
  will consistently use the ".html" extension in requests to the backend:

    location / {
        try_files $uri.html =404;
        proxy_pass http://backend;
    }

Review and testing appreciated.

-- 
Maxim Dounin