new confball
Merge tag '6.2.beta1' into t/15594/csage_autotools

Sage version 6.2.beta1
Trac #15594: Use autotools for csage

Use autotools instead of scons to build `c_lib`. After this change,
polybori is the only part of Sage using scons.

URL: http://trac.sagemath.org/15594
Reported by: ohanar
Ticket author(s): R. Andrew Ohana, Jeroen Demeyer
Reviewer(s): R. Andrew Ohana, Jeroen Demeyer