Difshells and difbuffers initialize close to equilibrium

In DifShell reinit set C (calcium) to Ceq. In DifBuffer reinit
calculate bFree (free buffer) and bBound (bound buffer) to steady
state value. This matches genesis implementation.

moose-core/biophysics/DifBuffer.cpp

@@ -439,6 +439,10 @@ void DifBuffer::vReinit( const Eref& e, ProcPtr p )
       assert( 0 );
     }
   
+  bFree_ = bTot_/(1+activation_*kf_/kb_);
+  prevFree_ = bFree_;
+  bBound_ = bTot_ - bFree_;
+  prevBound_ = bBound_;
 }
 
 void DifBuffer::vFluxFromIn(const Eref& e,double innerC, double innerThickness)

moose-core/biophysics/DifShell.cpp

@@ -323,6 +323,9 @@ void DifShell::vReinit( const Eref& e, ProcPtr p )
     default:
       assert( 0 );
     }
+  C_= Ceq_;
+  prevC_ = Ceq_;
+  concentrationOut()->send( e, C_ );
 }
 
 void DifShell::vProcess( const Eref & e, ProcPtr p )