Install Pidgin 2.10.9+ in our Wheezy branch

Pidgin 2.10.8 and later fixes various security issues. Once this is available in wheezy-security, we must drop our APT pinning on feature/wheezy that installs Pidgin 2.10.7 from wheezy-backports, and have that backport removed from the Debian archive as deprecated.

Parent Task: #6015 (closed)

Subtasks

#6646 (closed)

Original created by @intrigeri on 6645 (Redmine)

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