Firebird 2.5.3 updated in #Debian unstable with fb_guard lock file permissions fixes

Firebird 2.5.3 is updated in Debian unstable with minor security fixes
Here is the changelog :
* add patch tightening fb_guard lock file permissions (Closes: #767497) Thanks to Holger Levsen
*-super.postinst: tighten permissions on existing fbguard lock file
* declare conformance with Debian Policy 3.9.6