fix file leak for HEAD requests

u_char* is enough to keep file name

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

connection error should be logged with "connecting to upstream" action,
the bug was introduced in r1154

read EOF of header only responses in non-buffered proxying

there may be several "Connection" header lines and each may have several tokens

escape internal request URI in proxy_pass

style fix