Ierfc fails to be monotonically decreasing

[0xJepsen]

Ierfc is decreasing [FAIL]

  x1 923782811840660211
  y1 67648724918816645
  x2 923782811840660212
  y2 67648724918816646

x increases, but y doesn't decrease

[clemlak]

Same issue than #15, this is due to approximations, we'll investigate that later.