The patch removes the "files" section from package.json to avoid future issues
with missing files.  For package testing purposes, 'npm pack' is used instead
of plain 'tar' to simulate packaging more accurately.

The files loader.js and loader.mjs (introduced in f85b85094541 and 3c551b9721df)
were added to the packaged files list.

Also added stubs for Server.address()
This was done to prevent crashes in some popular frameworks like express

Supports both CommonJS and the new ES Modules system syntax e.g:

app.js:
const http = require('http')

app.mjs:
import http from "http"

Usage on Node 14.16.x and higher:
{
    "type": "external",
    "processes": {"spare": 0},
    "working_directory": '/project',
    "executable": "/usr/bin/env",
    "arguments": [
        "node",
        "--loader",
        "unit-http/require_shim.mjs"
        "--require",
        "unit-http/require_shim",
        "app.js"
    ]
}

Usage on Node 14.15.x and lower:
{
    "type": "external",
    "processes": {"spare": 0},
    "working_directory": '/project',
    "executable": "/usr/bin/env",
    "arguments": [
        "node",
        "--require",
        "unit-http/require_shim",
        "app.js"
    ]
}

This makes the "sed" instruction simpler and more portable, as the previous
variant didn't work well on BSD systems due to the "\s" metacharacter.

Thanks to Sergey A. Osokin <osa@FreeBSD.org.ru> for spotting this issue.

Also, this should prevent accidentally creating a version 1.0.0 package.

This partially reverts the optimisation introduced in 1d84b9e4b459 to avoid an
unpredictable block in nxt_unit_process_port_msg().  Under high load, this
function may never return control to its caller, and the external event loop
(in Node.js and Python asyncio) won't be able to process other scheduled
events.

To reproduce the issue, two request processing types are needed: 'fast' and
'furious'.  The 'fast' one simply returns a small response, while the 'furious'
schedules asynchronous calls to external resources.  Thus, if Unit is subjected
to a large amount of 'fast' requests, the 'furious' request processing freezes
until the high load ends.

The issue was found by Wu Jian Ping (@wujjpp) during Node.js stream
implementation discussion and relates to PR #502 on GitHub.

ServerRequest now inherit stream Readable object.  ServerResponse
provides 'writable' property.

Thanks to Wu Jian Ping (@wujjpp).

This closes #274, closes #317 issues and closes #502 PR on GitHub.

This fixes a crash on exit of Node.js application.  The crash reproduced
on Ubuntu 20.10 with Node.js v15.1.0.  Tests 'test_node_websockets_two_clients'
and 'test_node_websockets_7_13_1__7_13_2'.

The reason of the crash is using request struct which was already freed.

The issue was introduced in 5be509fda29e.

Warnings changed for debug messages.