Report fatal errors correctly in some keyword validators which didn't

Namely:
* "type" (draft v3),
* "not" (draft v4),
* "oneOf" (draft v4).

Fatal errors were "swallowed" in this case.

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
1.4.8

* Fix fatal error reporting with "type" (draft v3), "oneOf" (draft v4), "not"
  (draft v4): they were swallowed silently.

Francis Galiegue (1):
      Report fatal errors correctly in some keyword validators which didn't

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>