blitz::epsilon(__float128) = 0

Migrated from: https://sourceforge.net/p/blitz/bugs/67/

```
$ cat bug.cpp
#include <blitz/array.h>
#include <quadmath.h>

int main()
{
printf("%Qe\n", blitz::epsilon(__float128(0)));
}
```
```
$ g++ -lquadmath bug.cpp
$ ./a.out
0.000000e+00
```