Fix integer division

#### before

```
% OUTDIR=test/w TARGET=cl CHECK=clisp test/bin/buntest test/bun/G1*.bun
[OK] G1_Function (clisp test/w/G1_Function.cl)
[OK] G1_Grouping (clisp test/w/G1_Grouping.cl)
[OK] G1_If (clisp test/w/G1_If.cl)
[OK] G1_Let (clisp test/w/G1_Let.cl)
[FAILED] G1_Operator (clisp test/w/G1_Operator.cl)
*** - (EQUAL (/ X Y) 1) must evaluate to a non-NIL value.
[OK] G1_StringInterpolation (clisp test/w/G1_StringInterpolation.cl)
[OK] G1_Var (clisp test/w/G1_Var.cl)
[OK] G1_While (clisp test/w/G1_While.cl)
[OK] G1_WhileBreak (clisp test/w/G1_WhileBreak.cl)
# of OK: 8, # of FAILED: 1
```

#### after

```
% OUTDIR=test/w TARGET=cl CHECK=clisp test/bin/buntest test/bun/G1*.bun
[OK] G1_Function (clisp test/w/G1_Function.cl)
[OK] G1_Grouping (clisp test/w/G1_Grouping.cl)
[OK] G1_If (clisp test/w/G1_If.cl)
[OK] G1_Let (clisp test/w/G1_Let.cl)
[OK] G1_Operator (clisp test/w/G1_Operator.cl)
[OK] G1_StringInterpolation (clisp test/w/G1_StringInterpolation.cl)
[OK] G1_Var (clisp test/w/G1_Var.cl)
[OK] G1_While (clisp test/w/G1_While.cl)
[OK] G1_WhileBreak (clisp test/w/G1_WhileBreak.cl)
# of OK: 9, # of FAILED: 0
```