intbitset: no crash when intbitset is on rhs

* When an intbitset is on the right hand side of a foreign type
  operator (e.g. a set), do no longer crash with a segmentation
  fault, rather raises a TypeError.  (closes #1287)

Reported-by: Thorsten Schwander <thorsten.schwander@gmail.com>
Tested-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'maint-1.0' into maint-1.1

* maint-1.0:
  intbitset: no crash when intbitset is on rhs

Conflicts:
	modules/miscutil/lib/intbitset.c
	modules/miscutil/lib/intbitset.pyx

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>