Revert "BREAK install without boost (also without GSL)"

This reverts commit 243449d.

Author: terhorstd

libnestutil/sort.h

@@ -32,8 +32,10 @@
 
 #include "block_vector.h"
 
+#ifdef HAVE_BOOST
 #include "iterator_pair.h"
 #include <boost/sort/spreadsort/spreadsort.hpp>
+#endif
 
 #define INSERTION_SORT_CUTOFF 10 // use insertion sort for smaller arrays