Pop an integer off the stack
int SLang_pop_integer (int *i)
The SLang_pop_integer function removes an integer from the
top of the interpreter's run-time stack and returns its value via
the pointer i. If successful, it returns zero. However, if
the top stack item is not of type SLANG_INT_TYPE, or the
stack is empty, the function will return -1 and set
SLang_Error accordingly.
SLang_push_integer, SLang_pop_double