Reenable script cache from Server to Client

[Martii]

• Caching works well but GM kills it with channel.LOAD_BYPASS_CACHE and TM also uses no-cache to retrieve initial .user.js. According to TM author libraries (@require and @resource inclusions) don't use no-cache. Other engines to be tested after merge.

Applies to #432 and #249. Possible addition to #944 down the line. Regression managed from detection and revert in #894

[Martii]

SeaMonkey

Mozilla/5.0 (X11; Linux x86_64; rv:43.0) Gecko/20100101 SeaMonkey/2.40
GM Port (Greasemonkey Port 3.10.0.1rc1pre-sm.xpi) ENABLED

https://openuserjs.org/install/sizzle/The_GM_config_Unit_Test.user.js

GET /install/sizzle/The_GM_config_Unit_Test.user.js HTTP/1.0
Host: openuserjs.org
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:43.0) Gecko/20100101 SeaMonkey/2.40
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: keep-alive
Pragma: no-cache

HTTP/1.1 200 OK
X-Powered-By: Express
Strict-Transport-Security: max-age=31536000000; includeSubDomains
Cache-Control: public, max-age=86400, no-cache, no-transform, must-revalidate
Last-Modified: Sun, 01 May 2016 22:47:56 GMT
Expires: Wed, 05 Apr 2017 00:26:53 GMT
Content-Type: text/javascript; charset=UTF-8
Etag: "8m9xuugi348448cckskkogc0okowwgk8ggcsgwsg48ww0kscoggscck080808kcko4cs0ksg0gw8c4sc804wokwwo0scw4848o8"
Date: Tue, 04 Apr 2017 00:26:53 GMT
Connection: close
----------------------------------------------------------
https://openuserjs.org/src/libs/sizzle/GM_config.min.js

GET /src/libs/sizzle/GM_config.min.js HTTP/1.0
Host: openuserjs.org
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:43.0) Gecko/20100101 SeaMonkey/2.40
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: keep-alive
Pragma: no-cache

HTTP/1.1 200 OK
X-Powered-By: Express
Strict-Transport-Security: max-age=31536000000; includeSubDomains
Cache-Control: public, max-age=86400, no-cache, no-transform, must-revalidate
Last-Modified: Mon, 27 Mar 2017 18:51:46 GMT
Expires: Wed, 05 Apr 2017 00:26:53 GMT
Content-Type: text/javascript; charset=UTF-8
Etag: "jaredo4fwe0wws8ocsswgs8s4cs40swg8k8wcsk0cg4ggoow88so4csgk00gwc4kc8w0s44c0g0wkc0owkksss0sc4g80sk0wk4"
Date: Tue, 04 Apr 2017 00:26:54 GMT
Connection: close
----------------------------------------------------------