py: Fix bug in mpz_and function.

Addresses issue #610.

py/mpz.c

@@ -213,8 +213,8 @@ STATIC uint mpn_and(mpz_dig_t *idig, const mpz_dig_t *jdig, uint jlen, const mpz
         *idig = *jdig & *kdig;
     }
 
-    for (; jlen > 0; --jlen, ++idig) {
-        *idig = 0;
+    // remove trailing zeros
+    for (; idig > oidig && *idig == 0; --idig) {
     }
 
     return idig - oidig;

tests/basics/int-big-and.py

@@ -0,0 +1,8 @@
+print(0 & (1 << 80))
+print(0 & (1 << 80) == 0)
+print(bool(0 & (1 << 80)))
+
+#a = 0xfffffffffffffffffffffffffffff
+#print(a & (1 << 80))
+#print((a & (1 << 80)) >> 80)
+#print((a & (1 << 80)) >> 80 == 1)