if an earlier version of roundcube had already been installed, update to our target version
if an earlier version of roundcube had already been installed, update to our target version

fixes #195

jjz/mailinabox,pierreozoux/mailinabox,jjz/mailinabox,pierreozoux/mailinabox,ianberinger/mailinabox,nstanke/mailinabox,hnk/mailinabox,jprice/mailinabox,d5ve/mailinabox,pichak/mailinabox,pierreozoux/mailinabox,jjz/mailinabox,brocktice/mailinabox,m4rcs/mailinabox,jprice/mailinabox,brocktice/mailinabox,choltha/mailinabox,hnk/mailinabox,PortableTech/mailinabox,mail-in-a-box/mailinabox,PortableTech/mailinabox,jmedding/mailinabox,mboersma/mailinabox,jprice/mailinabox,jjz/mailinabox,choltha/mailinabox,d5ve/mailinabox,nstanke/mailinabox,mail-in-a-box/mailinabox,nstanke/mailinabox,m4rcs/mailinabox,Neopallium/mailinabox,b-deng/mailinabox,jprice/mailinabox,b-deng/mailinabox,ianberinger/mailinabox,choltha/mailinabox,mboersma/mailinabox,d5ve/mailinabox,nstanke/mailinabox,PortableTech/mailinabox,hnk/mailinabox,b-deng/mailinabox,mail-in-a-box/mailinabox,pichak/mailinabox,Toilal/mailinabox,PortableTech/mailinabox,Neopallium/mailinabox,mail-in-a-box/mailinabox,pierreozoux/mailinabox,brocktice/mailinabox,b-deng/mailinabox,jmedding/mailinabox,choltha/mailinabox,m4rcs/mailinabox,jjz/mailinabox,jmedding/mailinabox,mboersma/mailinabox,jmedding/mailinabox,d5ve/mailinabox,jmedding/mailinabox,brocktice/mailinabox,ianberinger/mailinabox,Toilal/mailinabox,PortableTech/mailinabox,Neopallium/mailinabox,Toilal/mailinabox,pichak/mailinabox,mboersma/mailinabox,choltha/mailinabox,Neopallium/mailinabox,m4rcs/mailinabox,jprice/mailinabox,brocktice/mailinabox,b-deng/mailinabox,mboersma/mailinabox,nstanke/mailinabox,d5ve/mailinabox,ianberinger/mailinabox,Neopallium/mailinabox,pierreozoux/mailinabox,pichak/mailinabox,ianberinger/mailinabox,hnk/mailinabox,Toilal/mailinabox,m4rcs/mailinabox