Change the defaults for shared_ptr.
Change the defaults for shared_ptr.

By default shared_ptr is now assumed to be
in the standard <memory> header and in the
std namespace.

Previously the way the ifdefs were structured if the appropriate
variable was not defined, it would default to <t1/memory>.

The new defaults are more future proof.

Change-Id: If457806191196be2b6425b8289ea7a3488a27445

stonier/ceres_solver,entylop/ceres-solver,ikoruk/ceres-solver,ysonggit/ceres-solver,kartikkumar/ceres-solver,kartikkumar/ceres-solver,ysonggit/ceres-solver,stonier/ceres_solver,stonier/ceres_solver,ikoruk/ceres-solver,DougFirErickson/ceres-solver,timfel/ceres-bin,DougFirErickson/ceres-solver,timfel/ceres-bin,ysonggit/ceres-solver,DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,whuaegeanse/ceres-solver,entylop/ceres-solver,ikoruk/ceres-solver,stonier/ceres_solver,timfel/ceres-bin,DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,ysonggit/ceres-solver,ikoruk/ceres-solver,kartikkumar/ceres-solver,kartikkumar/ceres-solver,entylop/ceres-solver,ikoruk/ceres-solver,whuaegeanse/ceres-solver,entylop/ceres-solver,timfel/ceres-bin