Proxy: split configured header names and values.
Proxy: split configured header names and values.

Previously, each configured header was represented in one of two ways,
depending on whether or not its value included any variables.

If the value didn't include any variables, then it would be represented
as as a single script that contained complete header line with HTTP/1.1
delimiters, i.e.:

     "Header: value\r\n"

But if the value included any variables, then it would be represented
as a series of three scripts: first contained header name and the ": "
delimiter, second evaluated to header value, and third contained only
"\r\n", i.e.:

     "Header: "
     "$value"
     "\r\n"

This commit changes that, so that each configured header is represented
as a series of two scripts: first contains only header name, and second
contains (or evaluates to) only header value, i.e.:

    "Header"
    "$value"

or

    "Header"
    "value"

This not only makes things more consistent, but also allows header name
and value to be accessed separately.

Signed-off-by: Piotr Sikora <ba6f3a1a6d7e1ecae91b31e93969cc392fbd0fdd@google.com>

hy0kl/nginx,hy0kl/nginx,hy0kl/nginx