Bug#926985: caffe: FTBFS, no output PDF file produced!

[Graham Inggs]

This is caused by #920459 in texlive-extra.  A workaround [1] that
skips building refman.pdf was uploaded to Ubuntu.


[1] 
https://launchpad.net/ubuntu/+source/caffe/1.0.0+git20180821.99bd997-2ubuntu1