Fix issues pointed out by @slazav.
Fix issues pointed out by @slazav.

This commit fixes several compilation issues with
ShiftedMatrixGeneralized. This bug has been present since
cd072f5b77 (June 2001), so it looks like this class has never worked as
advertised.

jperryhouts/dealii,nicolacavallini/dealii,pesser/dealii,danshapero/dealii,ESeNonFossiIo/dealii,Arezou-gh/dealii,gpitton/dealii,nicolacavallini/dealii,andreamola/dealii,naliboff/dealii,EGP-CIG-REU/dealii,gpitton/dealii,nicolacavallini/dealii,nicolacavallini/dealii,naliboff/dealii,maieneuro/dealii,JaeryunYim/dealii,kalj/dealii,danshapero/dealii,danshapero/dealii,Arezou-gh/dealii,nicolacavallini/dealii,andreamola/dealii,sairajat/dealii,ESeNonFossiIo/dealii,gpitton/dealii,spco/dealii,shakirbsm/dealii,sairajat/dealii,shakirbsm/dealii,spco/dealii,maieneuro/dealii,Arezou-gh/dealii,danshapero/dealii,gpitton/dealii,JaeryunYim/dealii,jperryhouts/dealii,shakirbsm/dealii,maieneuro/dealii,danshapero/dealii,naliboff/dealii,nicolacavallini/dealii,Arezou-gh/dealii,shakirbsm/dealii,maieneuro/dealii,kalj/dealii,pesser/dealii,sairajat/dealii,spco/dealii,naliboff/dealii,JaeryunYim/dealii,pesser/dealii,pesser/dealii,ESeNonFossiIo/dealii,angelrca/dealii,EGP-CIG-REU/dealii,angelrca/dealii,JaeryunYim/dealii,gpitton/dealii,EGP-CIG-REU/dealii,jperryhouts/dealii,angelrca/dealii,pesser/dealii,andreamola/dealii,ESeNonFossiIo/dealii,shakirbsm/dealii,shakirbsm/dealii,shakirbsm/dealii,JaeryunYim/dealii,jperryhouts/dealii,JaeryunYim/dealii,EGP-CIG-REU/dealii,Arezou-gh/dealii,kalj/dealii,ESeNonFossiIo/dealii,andreamola/dealii,jperryhouts/dealii,jperryhouts/dealii,naliboff/dealii,gpitton/dealii,spco/dealii,nicolacavallini/dealii,JaeryunYim/dealii,sairajat/dealii,andreamola/dealii,maieneuro/dealii,sairajat/dealii,ESeNonFossiIo/dealii,sairajat/dealii,kalj/dealii,pesser/dealii,spco/dealii,jperryhouts/dealii,spco/dealii,pesser/dealii,EGP-CIG-REU/dealii,andreamola/dealii,kalj/dealii,danshapero/dealii,kalj/dealii,maieneuro/dealii,naliboff/dealii,angelrca/dealii,andreamola/dealii,spco/dealii,maieneuro/dealii,sairajat/dealii,Arezou-gh/dealii,Arezou-gh/dealii,angelrca/dealii,naliboff/dealii,gpitton/dealii,angelrca/dealii,EGP-CIG-REU/dealii,angelrca/dealii,danshapero/dealii,ESeNonFossiIo/dealii,kalj/dealii,EGP-CIG-REU/dealii