base: use uintptr_t for hash type

Use uintptr_t for hash type; this is consistent with CoreFoundation, which uses
32-bit integers on 32-bit platforms for the hash code, and 64-bit integers on
64-bit platforms. (libheimbase is modelled on CoreFoundation.)

Previously we used unsigned long, which would have the same behavior on
LP32/LP64 systems, but not on Windows (where unsigned long is 32-bits on 64-bit
platforms).

lib/base/heimbase.h

@@ -184,7 +184,7 @@ heim_get_tid(heim_object_t object);
 int
 heim_cmp(heim_object_t a, heim_object_t b);
 
-unsigned long
+uintptr_t
 heim_get_hash(heim_object_t ptr);
 
 void