fix file leak for HEAD requests

the "proxy_hide_header" and "fastcgi_hide_header" directives did not
hide response header lines whose name was longer than 32 characters

allow to append charset to the "Content-Type" header

response to the HEAD request should be a header only

escape internal request URI in proxy_pass

change ngx_conf_merge_ptr_value() and update fastcgi_catch_stderr

use %v for ngx_variable_value_t in ngx_sprintf(),
this fixes nginx on FreeBSD/sparc64

ignore meaningless bits in CIDR and warn about them

add_header changes:
"Last-Modified", "Cache-Control" and "Expires" headers use specific handlers

fix case when two directives
    proxy_pass   http://backend;
    proxy_pass   https://backend;
both use one port - 80 or 443, that was defined first.