Minz allow parallel sessions (#3096)

* Minz allow parallel sessions

#fix https://github.com/FreshRSS/FreshRSS/issues/3093

* Array optimisation

* Array optimisation missing

* Reduce direct access to $_SESSION except in install process

* Fix session start headers warning

* Use cookie only the first time the session is started:
`PHP Warning:  session_start(): Cannot start session when headers
already sent in /var/www/FreshRSS/lib/Minz/Session.php on line 39`

* New concept of volatile session for API calls

Optimisation: do not use cookies or local storage at all for API calls
without a Web session
Fix warning:

```
PHP Warning:  session_destroy(): Trying to destroy uninitialized session
in Unknown on line 0
```

* Only call Minz_Session::init once in our index

It was called twice (once indirectly via FreshRSS->init())

* Whitespace

* Mutex for notifications

Implement mutex for notifications
https://github.com/FreshRSS/FreshRSS/pull/3208#discussion_r499509809

* Typo

* Install script is not ready for using Minz_Session

1 files changed, 3 insertions, 2 deletions

diff --git a/p/i/index.php b/p/i/index.php
index 35e53ec5e..d1d56bbb9 100755
--- a/p/i/index.php
+++ b/p/i/index.php
@@ -27,8 +27,6 @@ if (file_exists(DATA_PATH . '/do-install.txt')) {
 	require(APP_PATH . '/install.php');
 } else {
 	session_cache_limiter('');
-	Minz_Session::init('FreshRSS');
-	Minz_Session::_param('keepAlive', 1);	//To prevent the PHP session from expiring
 
 	if (!file_exists(DATA_PATH . '/no-cache.txt')) {
 		require(LIB_PATH . '/http-conditional.php');
@@ -38,6 +36,8 @@ if (file_exists(DATA_PATH . '/do-install.txt')) {
 			@filemtime(join_path(DATA_PATH, 'config.php'))
 		);
 		if (httpConditional($dateLastModification, 0, 0, false, PHP_COMPRESSION, true)) {
+			Minz_Session::init('FreshRSS');
+			Minz_Session::_param('keepAlive', 1);	//To prevent the PHP session from expiring
 			exit();	//No need to send anything
 		}
 	}
@@ -65,6 +65,7 @@ if (file_exists(DATA_PATH . '/do-install.txt')) {
 		if ($result === true) {
 			$front_controller = new FreshRSS();
 			$front_controller->init();
+			Minz_Session::_param('keepAlive', 1);	//To prevent the PHP session from expiring
 			$front_controller->run();
 		} else {
 			$error = $result;