Do not upgrade if PHP version is not supported by new version

[sokai]

Steps to reproduce

1. Installed version: 10.0.1 (beta)
2. Upgraded to 11.0 beta 2 via web-updater

Expected behaviour

Disallow the upgrade to a newer version of Nextcloud if that doesn't support current installed but required software.

Actual behaviour

After the successful upgrade following message is shown:

This version of Nextcloud requires at least PHP 5.6.0
You are currently running 5.5.9-1ubuntu4.20. Please update your PHP version.

Server configuration

Operating system:
Ubuntu 14.04.5 LTS (yesiknowishouldupgrade)

Web server:
Apache/2.4.7 (Ubuntu)

Database:
mysql Ver 14.14 Distrib 5.5.53, for debian-linux-gnu (x86_64) using readline 6.3

PHP version:
PHP 5.5.9-1ubuntu4.20 (cli) (built: Oct 3 2016 13:00:37)

Nextcloud version: (see Nextcloud admin page)
10.0.1 (beta)

Updated from an older Nextcloud/ownCloud or fresh install:
(can't remember …)

Where did you install Nextcloud from:
(can't remember …)

Signing status:

Signing status

This version of Nextcloud requires at least PHP 5.6.0
You are currently running 5.5.9-1ubuntu4.20. Please update your PHP version.

PS: How can I now roll back to my working 10.0.1 (beta) …!? :-| thx!

[LukasReschke]

Dupe of nextcloud/updater#53

PS: How can I now roll back to my working 10.0.1 (beta) …!? :-| thx!

Replace all files except data and config with the 10.0.1 code.

[sokai]

@LukasReschke Thx!

Conc. the restore: I found the backup in my data folder as nextcloud-9.1.0.13 and restored that successfully…

Conc. the dupe: Sry, I missed that. (Should I add a comment to nextcloud/updater#53)?