Ported scoplib to use isl_val * instead of isl_int

1) The isl_int -> isl_val changes are the ones Tobias suggested.
   One additional isl_val_free is added (and needed)
2) Three scoplib_vector_free are added, maybe we would need even
   more (and matrix_free) but it's hard to place them right.
3) Cleaned the includes (and removed 'extern C')

This fixes the broken compilation for the scoplib import and export.

Contributed-by: Johannes Doerfert <doerfert@cs.uni-saarland.de>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@203500 91177308-0d34-0410-b5e6-96231b3b80d8