* fixed bugs 3cd: structure slot readers perform type check if the
slot can have an invalid value (i.e. it is either not initialized
or can be written with a less specific slot writer).
+ * bug fix: the compiler now traps array references to elements off
+ the end of an array; previously, the bounds checking in some
+ circumstances could go off-by-one.
planned incompatible changes in 0.8.x:
* (not done yet, but planned:) When the profiling interface settles