Add #include needed for _mm_mfence() intrinsic on ia64.

Hopefully this fixes the build failure on buildfarm member dugong.
Fix memory barrier support on icc on ia64, 2nd attempt.

Itanium doesn't have the mfence instruction - that's a 386 thing. Use the
"mf" instruction instead.

This reverts the previous commit to add "#include <emmintrinsic.h>"; the
problem was not with a missing #include.
Fix lack of message pluralization
Add coverage/ to .gitignore