We want to switch to the about me capplet which is in upstream control-center
since 2.12, which will allow us to replace 3 of our homegrown capplets (login
photo, password and about myself). To do this properly,  we need to be able to
use the userhelper mechanism to update the gecos information. 

Since userhelper_runv() is not available in a library, the next best way to
achieve this in a nonintrusive way is to make userinfo accept the gecos data on
the commandline, and not open the dialog in that case.

The attached patch does that.