ideally cause the compiler to give an error.  Right now 6g
warns about large shifts but does not give an error.  This CL
removes the out of range shift from shift.go, so that it will
work with gccgo, and adds a test case in bugs/ to be fixed at
a later date.

R=ken,r
DELTA=23  (9 added, 14 deleted, 0 changed)
OCL=16085
CL=16088