Fix reference count bug affecting mpq_numref and mpq_denref.
Fix reference count bug affecting mpq_numref and mpq_denref.

jtobey/javascript-bignum,angeni8/javascript-bignum,angeni8/javascript-bignum,jtobey/javascript-bignum,angeni8/javascript-bignum,angeni8/javascript-bignum,jtobey/javascript-bignum,angeni8/javascript-bignum,angeni8/javascript-bignum,jtobey/javascript-bignum,jtobey/javascript-bignum,jtobey/javascript-bignum