Compute a hash-code for this range. Two ranges with equal begin and end
points (using eql?), and the same #exclude_end? value will generate the
same hash-code.
See also Object#hash.
static VALUE
range_hash(VALUE range)
{
st_index_t hash = EXCL(range);
VALUE v;
hash = rb_hash_start(hash);
v = rb_hash(RANGE_BEG(range));
hash = rb_hash_uint(hash, NUM2LONG(v));
v = rb_hash(RANGE_END(range));
hash = rb_hash_uint(hash, NUM2LONG(v));
hash = rb_hash_uint(hash, EXCL(range) << 24);
hash = rb_hash_end(hash);
return LONG2FIX(hash);
}