[igraph] Unable to install from PPA in Ubuntu 13.04

[Bradford Boyle]

The default version of igraph in Ubuntu 13.04 is 0.5.4-2. I added the
igraph PPA to grab igraph 0.6.5-2. The package libigraph0 depends on
libgmp3c2 which is an obsolete package and not available on 13.04.

On a clean install of 13.04, the following steps will reproduce the bug:

sudo add-apt-repository ppa:igraph/ppa
sudo apt-get update
sudo apt-get install libigraph0

Output of the above steps:

The following packages have unmet dependencies:
 libigraph0 : Depends: libgmp3c2 but it is not installable
E: Unable to correct problems, you have held broken packages.

Bradford