Fixed average h.t.c computation in HeatTransfer2phDB model

git-svn-id: https://svn.code.sf.net/p/thermopower/svn/trunk@176 80daafeb-7430-0410-91d5-8b30b0bbd841
Fixed parameters in TestHeatTransfer2phDBa and TestHeatTransfer2phDBb;

git-svn-id: https://svn.code.sf.net/p/thermopower/svn/trunk@177 80daafeb-7430-0410-91d5-8b30b0bbd841