[DRE-maint] Bug#733106: ruby-exif: Unreliable build

[Christian Hofstaedtler]

Package: ruby-exif
Severity: serious
Justification: Policy 4.6

Dear Maintainer,

ruby-exif fails to catch build errors, causing partially-usable packages
to enter the archive.

Please see these buildd logs (look for "extconf.rb failed"):

https://buildd.debian.org/status/fetch.php?pkg=ruby-exif&arch=kfreebsd-amd64&ver=0.1.2-20&stamp=1338324477

https://buildd.debian.org/status/fetch.php?pkg=ruby-exif&arch=kfreebsd-i386&ver=0.1.2-20&stamp=1338320935

https://buildd.debian.org/status/fetch.php?pkg=ruby-exif&arch=hurd-i386&ver=0.1.2-20&stamp=1338322303

  Christian