Reinstating PETSC_DIR in package build
Reinstating PETSC_DIR in package build

Change purely in packaging system: with the move to 3.6.3 on the standard Ubuntu LTS build for Fluidity, the debian packaging method needs PETSC_DIR setting again. For builds NOT on the standard Fluidity Ubuntu LTS platform, PETSC_DIR may need to be reset to whatever local value is required, but since most builds will take place on the standard Fluidity builders this should, in most cases, work.
jrper/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity