Use uintptr_t for pointer casts in Swig files (#1278)

Use uintptr_t for pointer casts in Swig files (#1278)

CVC4's Swig interface files were casting pointers to longs in multiple
instances. The problem with that is that on certain platforms *cough*
Windows/MinGW *cough* long is only 32-bit even when compiling a 64-bit
executable (they use the LLP64 data model). This made the compilation of
language bindings fail with MinGW. This commit changes the types to
uintptr_t defined in Swig's stdint.i.