Warn about disabled schur specializations.
Warn about disabled schur specializations.

This commit brought to you from 30,000ft.

vedanshu95/ceres-solver,jmwalls/ceres-solver-fork,jmwalls/ceres-solver-fork,DougFirErickson/ceres-solver,kartikkumar/ceres-solver,timfel/ceres-bin,jmwalls/ceres-solver-fork,pritasam/ceres-solver,timfel/ceres-bin,ikoruk/ceres-solver,dkogan/ceres,vedanshu95/ceres-solver,kartikkumar/ceres-solver,DougFirErickson/ceres-solver,arnaudgelas/ceres-solver,dkogan/ceres,arnaudgelas/ceres-solver,ikoruk/ceres-solver,ysonggit/ceres-solver,whuaegeanse/ceres-solver,ikoruk/ceres-solver,entylop/ceres-solver,ysonggit/ceres-solver,DougFirErickson/ceres-solver,whuaegeanse/ceres-solver,whuaegeanse/ceres-solver,caomw/ceres-solver,techoe/ceres-solver,techoe/ceres-solver,ysonggit/ceres-solver,pritasam/ceres-solver,ysonggit/ceres-solver,techoe/ceres-solver,stonier/ceres_solver,entylop/ceres-solver,pritasam/ceres-solver,whuaegeanse/ceres-solver,entylop/ceres-solver,timfel/ceres-bin,arnaudgelas/ceres-solver,timfel/ceres-bin,kartikkumar/ceres-solver,caomw/ceres-solver,entylop/ceres-solver,jmwalls/ceres-solver-fork,kartikkumar/ceres-solver,caomw/ceres-solver,ikoruk/ceres-solver,stonier/ceres_solver,stonier/ceres_solver,stonier/ceres_solver,DougFirErickson/ceres-solver,ikoruk/ceres-solver,vedanshu95/ceres-solver,dkogan/ceres