Add test for whether the SAHooks type is available from shapelib, and
if the resulting HAVE_SAHOOKS CMake variable is true,
then #define the HAVE_SAHOOKS C macro for src/plmap.c.
Tested by Alan W. Irwin <firstname.lastname@example.org> on Linux
by checking that the example 19 result (for shapelib 1.3.0) does not
generate the misleading "Unable to open" error messages
from shapelib that you get when HAVE_SAHOOKS is not true.