Free the WKB-memory allocated by GEOS

[lzzgeo]

I have programed some codes on windows XP by using VC 8.0. when I created WKB memory bolck by using GEOSGeomToWKB_buf()，and freed it by using std::free(), the application will be corrupted. the source codes like this:

LONG nSize(0);
GEOSGeometry *g1(NULL);
unsigned char * pWkb(NULL);

creating the geometry g1 ...

pWkb = GEOSGeomToWKB_buf(g1, (size_t*)&nSize);

free(pWkb); will triger some error
pWkb = NULL;

GEOSGeom_destroy(g1);

so, I think we should add a function to free memory block allocated by GEOS， like this:

add the following codes into geos_c.h:
extern void GEOS_DLL GEOS_destroy(void *p);

add the following codes into geos_c.cpp:
void GEOS_destroy(void *a) {

return std::free(a);

}

it will work pretty good!

[hobu]

Duplicate #249