Added parsing of velocityBasis from XML

<transport> 
	<speciesDiffusivity>
		<velocityBasis basis="mass">
Other valid values are "mole" or a species name.
This is loaded into LiquidTransportParams and then copied into
LiquidTransport in the initLiquidTransport() method.

Cantera/src/transport/LiquidTransport.cpp

@@ -185,6 +185,7 @@ namespace Cantera {
     int k;
     // constant substance attributes
     m_thermo = tr.thermo;
+    m_velocityBasis = tr.velocityBasis;
     m_nsp   = m_thermo->nSpecies();
     m_tmin  = m_thermo->minTemp();
     m_tmax  = m_thermo->maxTemp();

Cantera/src/transport/TransportFactory.cpp

@@ -1116,6 +1116,31 @@ namespace Cantera {
 	  throw TransportDBError( linenum, 
 				  "missing <compositionDependence> node for <" 
 				  + tranTypeNode.name() + "> node." );
+	}
+	/* Allow a switch between mass-averaged, mole-averaged 
+	 * and solvent specified reference velocities.  
+	 * XML code within the transportProperty node 
+	 * (i.e. within <viscosity>) should read as follows
+	 * <velocityBasis basis="mass"> <!-- mass averaged -->
+	 * <velocityBasis basis="mole"> <!-- mole averaged -->
+	 * <velocityBasis basis="H2O">  <!-- H2O solvent -->
+	 */
+	if ( tranTypeNode.hasChild("velocityBasis")) {
+	  std::string velocityBasis = 
+	    tranTypeNode.child("velocityBasis").attrib("basis");
+	  if ( velocityBasis == "mass" ) 
+	    trParam.velocityBasis = VB_MASSAVG;
+	  else if ( velocityBasis == "mole" ) 
+	    trParam.velocityBasis = VB_MOLEAVG;
+	  else if ( trParam.thermo->speciesIndex( velocityBasis ) > 0 ) 
+	    trParam.velocityBasis = trParam.thermo->speciesIndex( velocityBasis ) ;
+	  else {
+	    int linenum;
+	    throw TransportDBError( linenum, "Unknown attribute " + velocityBasis + " for <velocityBasis> node. ");
+	}
+
+	  
+
 	}
       }
     }

Cantera/src/transport/TransportParams.h

@@ -19,7 +19,7 @@ namespace Cantera {
 
     public:
 
-        TransportParams() : thermo(0), xml(0) {}
+        TransportParams() : thermo(0), xml(0), velocityBasis(VB_MASSAVG) {}
         virtual ~TransportParams();
         int nsp_;
 
@@ -27,6 +27,10 @@ namespace Cantera {
         thermo_t* thermo;
         vector_fp        mw;
 
+	//! A basis for the average velocity can be specified. 
+	//! Valid bases include "mole" "mass" and species names.
+	int velocityBasis;
+
 	//minimum and maximum temperatures for parameter fits
         doublereal tmax, tmin;
         int mode_;