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).

Fix for proxy_store leaving temporary files for subrequests.

Temporary files might not be removed if the "proxy_store" or "fastcgi_store"
directives were used for subrequests (e.g. ssi includes) and client closed
connection prematurely.

Non-active subrequests are finalized out of the control of the upstream
module when client closes a connection.  As a result, the code to remove
unfinished temporary files in ngx_http_upstream_process_request() wasn't
executed.

Fix is to move relevant code into ngx_http_upstream_finalize_request() which
is called in all cases, either directly or via the cleanup handler.

Removed r->cache/r->cached dependencies in range filter.  This is
a layering violation, use correct offset calculations instead.

If header filter postponed processing of a header by returning NGX_AGAIN
and not moved u->buffer->pos, previous check incorrectly assumed there
is additional space and did another recv() with zero-size buffer.  This
resulted in "upstream prematurely closed connection" error instead
of correct "upstream sent too big header" one.

Patch by Feibo Li.