Move raw packet printing into print-ascii.c.

We don't necessiciarly want to sandbox this code, but the truly paranoid
might and it reduces the number of interfaces to the print code.
Split util.c into print and non-print fuctions.

Currently some dissectors use error().  This is certainly a bug.
Remove most direct comparisons to the end of the packet pointer.
In particular, attempt to remove all cases where a pointer that is
potentialy past that pointer are created.

This is largely accomplished through the use of existing TTEST(2) and
TCHECK(2) macros plus some new PACKET_ macros.

Add commets about a number of overflows caused by slightly wrong
comparisons.