changed travis build matrix to use precompiled headers
changed travis build matrix to use precompiled headers

tpaviot/oce,BenoitPerrot/oce,BenoitPerrot/oce,BenoitPerrot/oce,tpaviot/oce,tpaviot/oce,BenoitPerrot/oce,BenoitPerrot/oce,tpaviot/oce,tpaviot/oce