Fix DTrace/SystemTap-related formatting

Thanks to Michał Ptaszek for bringing this embarrassing formatting error to
my attention.  Many DTrace/SystemTap trace strings are incorrectly
truncated at 4/8 bytes, depending on the CPU word size.  This patch expands
the work from commit d032e097 by zheng siyao.

Michał's report to the erlang-bugs list can be found at:
http://erlang.org/pipermail/erlang-bugs/2014-March/004250.html

cc: @paulgray @vinoski