I was able to get rid of the earlier fglrx files with sudo apt-get purge fglrx. The proprietary installation proceeded but failed. Here is the output from the install log

Supported adapter detected.
Check if system has the tools required for installation.
Uninstalling any previously installed drivers.

Creating symlink /var/lib/dkms/fglrx/13.251/source ->

DKMS: add completed.

Kernel preparation unnecessary for this kernel. Skipping...

Building module:
cleaning build area....
cd /var/lib/dkms/fglrx/13.251/build; sh make.sh --nohints --uname_r=3.11.0-15-generic --norootcheck....(bad exit status: 1)
[Error] Kernel Module : Failed to build fglrx-13.251 with DKM

Deleting module version: 13.251
completely from the DKMS tree.