Allow comparison == and != of TriaAccessorBase with different tria
Allow comparison == and != of TriaAccessorBase with different tria

It is well-defined to check for equality and inequality of TriaAccessorBase (cell_iterator types) that belong to different triangulations. Those are simply unequal. This is necessary e.g. for comparing with a default constructed cell_iterator variable. Of course, operator < is still undefined.

ESeNonFossiIo/dealii,jperryhouts/dealii,msteigemann/dealii,jperryhouts/dealii,lue/dealii,sriharisundar/dealii,lue/dealii,pesser/dealii,mtezzele/dealii,spco/dealii,danshapero/dealii,lpolster/dealii,sriharisundar/dealii,Arezou-gh/dealii,maieneuro/dealii,msteigemann/dealii,spco/dealii,lue/dealii,shakirbsm/dealii,maieneuro/dealii,rrgrove6/dealii,EGP-CIG-REU/dealii,lue/dealii,EGP-CIG-REU/dealii,msteigemann/dealii,jperryhouts/dealii,gpitton/dealii,ESeNonFossiIo/dealii,shakirbsm/dealii,maieneuro/dealii,rrgrove6/dealii,angelrca/dealii,kalj/dealii,spco/dealii,mac-a/dealii,rrgrove6/dealii,pesser/dealii,johntfoster/dealii,sriharisundar/dealii,sairajat/dealii,kalj/dealii,gpitton/dealii,adamkosik/dealii,YongYang86/dealii,msteigemann/dealii,ESeNonFossiIo/dealii,msteigemann/dealii,maieneuro/dealii,sriharisundar/dealii,rrgrove6/dealii,sairajat/dealii,natashasharma/dealii,lpolster/dealii,natashasharma/dealii,adamkosik/dealii,gpitton/dealii,spco/dealii,EGP-CIG-REU/dealii,adamkosik/dealii,sriharisundar/dealii,lpolster/dealii,nicolacavallini/dealii,gpitton/dealii,kalj/dealii,ibkim11/dealii,lue/dealii,jperryhouts/dealii,JaeryunYim/dealii,kalj/dealii,ibkim11/dealii,JaeryunYim/dealii,Arezou-gh/dealii,mtezzele/dealii,pesser/dealii,flow123d/dealii,flow123d/dealii,mtezzele/dealii,mtezzele/dealii,EGP-CIG-REU/dealii,ibkim11/dealii,ESeNonFossiIo/dealii,mac-a/dealii,mtezzele/dealii,natashasharma/dealii,lue/dealii,spco/dealii,adamkosik/dealii,pesser/dealii,flow123d/dealii,YongYang86/dealii,johntfoster/dealii,JaeryunYim/dealii,ESeNonFossiIo/dealii,andreamola/dealii,danshapero/dealii,naliboff/dealii,angelrca/dealii,flow123d/dealii,sriharisundar/dealii,mac-a/dealii,kalj/dealii,mac-a/dealii,shakirbsm/dealii,naliboff/dealii,mac-a/dealii,natashasharma/dealii,Arezou-gh/dealii,YongYang86/dealii,nicolacavallini/dealii,spco/dealii,msteigemann/dealii,andreamola/dealii,spco/dealii,flow123d/dealii,mac-a/dealii,shakirbsm/dealii,sriharisundar/dealii,nicolacavallini/dealii,sairajat/dealii,gpitton/dealii,JaeryunYim/dealii,mtezzele/dealii,maieneuro/dealii,johntfoster/dealii,kalj/dealii,sairajat/dealii,EGP-CIG-REU/dealii,shakirbsm/dealii,johntfoster/dealii,ibkim11/dealii,danshapero/dealii,Arezou-gh/dealii,kalj/dealii,angelrca/dealii,YongYang86/dealii,gpitton/dealii,angelrca/dealii,johntfoster/dealii,naliboff/dealii,rrgrove6/dealii,naliboff/dealii,gpitton/dealii,YongYang86/dealii,natashasharma/dealii,Arezou-gh/dealii,adamkosik/dealii,ESeNonFossiIo/dealii,JaeryunYim/dealii,johntfoster/dealii,ESeNonFossiIo/dealii,ibkim11/dealii,sairajat/dealii,adamkosik/dealii,danshapero/dealii,andreamola/dealii,andreamola/dealii,jperryhouts/dealii,andreamola/dealii,nicolacavallini/dealii,pesser/dealii,danshapero/dealii,johntfoster/dealii,nicolacavallini/dealii,natashasharma/dealii,EGP-CIG-REU/dealii,pesser/dealii,jperryhouts/dealii,rrgrove6/dealii,lpolster/dealii,danshapero/dealii,rrgrove6/dealii,msteigemann/dealii,flow123d/dealii,flow123d/dealii,naliboff/dealii,lue/dealii,maieneuro/dealii,JaeryunYim/dealii,angelrca/dealii,adamkosik/dealii,EGP-CIG-REU/dealii,YongYang86/dealii,shakirbsm/dealii,maieneuro/dealii,Arezou-gh/dealii,andreamola/dealii,YongYang86/dealii,angelrca/dealii,natashasharma/dealii,lpolster/dealii,mac-a/dealii,sairajat/dealii,nicolacavallini/dealii,shakirbsm/dealii,jperryhouts/dealii,JaeryunYim/dealii,angelrca/dealii,Arezou-gh/dealii,ibkim11/dealii,pesser/dealii,danshapero/dealii,lpolster/dealii,ibkim11/dealii,naliboff/dealii,mtezzele/dealii,nicolacavallini/dealii,lpolster/dealii,andreamola/dealii,naliboff/dealii,sairajat/dealii