Fix inverse_discrete_quantile for large guess

If `guess` passed to `inverse_discrete_quantile` cannot be represented
as floating point number, it is possible that `guess + 1` or `guess - 1`
does not change the value at all and we are stuck in infinite loop
inside `round_to_floor` or `round_to_ceil`.  Fix this by
increase/decrease more than 1 in these cases.

Example code to reproduce this:
```c++
boost::math::binomial_distribution<> dist(9079765771874083840, 0.561815);
boost::math::quantile(dist, 0.0365346);
```

include/boost/math/distributions/detail/inv_discrete_quantile.hpp

@@ -302,15 +302,17 @@ inline typename Dist::value_type round_to_floor(const Dist& d, typename Dist::va
    //
    while(result != 0)
    {
-      cc = result - 1;
+      cc = result;
+      for (typename Dist::value_type d = 1; cc == result; d += 1)
+      {
+         cc = result - d;
+      }
       if(cc < support(d).first)
          break;
       pp = c ? cdf(complement(d, cc)) : cdf(d, cc);
-      if(pp == p)
-         result = cc;
-      else if(c ? pp > p : pp < p)
+      if(c ? pp > p : pp < p)
          break;
-      result -= 1;
+      result = cc;
    }
 
    return result;
@@ -336,15 +338,17 @@ inline typename Dist::value_type round_to_ceil(const Dist& d, typename Dist::val
    //
    while(true)
    {
-      cc = result + 1;
+      cc = result;
+      for (typename Dist::value_type d = 1; cc == result; d += 1)
+      {
+         cc = result + d;
+      }
       if(cc > support(d).second)
          break;
       pp = c ? cdf(complement(d, cc)) : cdf(d, cc);
-      if(pp == p)
-         result = cc;
-      else if(c ? pp < p : pp > p)
+      if(c ? pp < p : pp > p)
          break;
-      result += 1;
+      result = cc;
    }
 
    return result;