[DRE-maint] Bug#909775: redmine: "relax some dependencies" patch is too relaxed for mysql2

[Hashem Nasarat]

Source: redmine
Severity: important

Dear Maintainer,

The aforementioned patch has:

-        gem "mysql2", "~> 0.4.6", :platforms => [:mri, :mingw, :x64_mingw]
+        gem "mysql2", "~> 0.4", :platforms => [:mri, :mingw, :x64_mingw]

However, this should be "~> 0.4.0" because redmine 3.x is only compatible with
rails 4, and mysql2 0.5 is only compatible with rails 5.

Currently ruby-mysql2 package in Debian is 0.4.5, so some patch for this is
still needed.

This can cause problems:

1. Install a plugin, e.g.
https://www.redmineup.com/pages/help/installation/how-to-install-redmine-plugins-on-linux
2. Run bundle install
3. bundle will update mysql2 to 0.5.x
4. redmine will no longer start



-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.18.0-1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)