*) Fixed incorrect ngx_cpystrn() usage in ngx_http_*_process_header().

   This resulted in a disclosure of previously freed memory if upstream
   server returned specially crafted response, potentially exposing
   sensitive information.

   Reported by Matthew Daley.

*) Headers with null character are now rejected.

   Headers with NUL character aren't allowed by HTTP standard and may cause
   various security problems.  They are now unconditionally rejected.

Fix of rbtree lookup on hash collisions.

Previous code incorrectly assumed that nodes with identical keys are linked
together.  This might not be true after tree rebalance.

Patch by Lanshun Zhou.

*) Renamed constants and fixed off-by-one error in "msie_padding on"
   handling.

*) Added support for the 307 Temporary Redirect.

*) Fixed build with embedded perl and --with-openssl.

*) Configure: moved icc detection before gcc.  New versions of icc
   confuse auto/cc/name due to introduced handling of a "icc -v".

Core: protection from cycles with named locations and post_action.

Now redirects to named locations are counted against normal uri changes
limit, and post_action respects this limit as well.  As a result at least
the following (bad) configurations no longer trigger infinite cycles:

1. Post action which recursively triggers post action:

    location / {
        post_action /index.html;
    }

2. Post action pointing to nonexistent named location:

    location / {
        post_action @nonexistent;
    }

3. Recursive error page for 500 (Internal Server Error) pointing to
   a nonexistent named location:

    location / {
        recursive_error_pages on;
        error_page 500 @nonexistent;
        return 500;
    }

Variables: honor no_cacheable for not_found variables.

Variables with the "not_found" flag set follow the same rules as ones with
the "valid" flag set.  Make sure ngx_http_get_flushed_variable() will flush
non-cacheable variables with the "not_found" flag set.

This fixes at least one known problem with $args not available in a subrequest
(with args) when there were no args in the main request and $args variable was
queried in the main request (reported by Laurence Rowe aka elro on irc).

Also this eliminates unneeded call to ngx_http_get_indexed_variable() in
cacheable case (as it will return cached value anyway).