appearance preferences cannot find aurora theme engine

[Corollax]

Version Tested:
* Ubuntu Raring and Ubuntu Saucy
* MATE 1.6.0
* gtk2-engines-aurora_1.5.1-3_amd64

Expected Result:
* Appearance Preferences should silently enable the selected theme.
* libaurora.so should be installed at /usr/lib/x86_64-linux-gnu/gtk-2.0/2.10.0/engines/libaurora.so

Observed Result:
* Appearance Preferences reports "This theme will not look as intended because the required GTK+ theme engine 'aurora' is not installed."
* libaurora.so was installed at /usr/lib/gtk-2.0/2.10.0/engines/libaurora.so

Reproduction Steps:
* Install a theme (such as WildMint) dependent on the aurora theme engine and select it with Appearance Preferences (OR):
# apt-get install gtk2-engines-aurora
$ find /usr/lib/ -name ‘libaurora.so’

Obvious Workaround:
# ln -s /usr/lib/gtk-2.0/2.10.0/engines/libaurora.so /usr/lib/x86_64-linux-gnu/gtk-2.0/2.10.0/engines/libaurora.so

[Launchpad Janitor (janitor)]

[Expired for gtk2-engines-aurora (Ubuntu) because there has been no activity for 60 days.]