Reduce misuse of fatalerror.h

Reduce misuse of fatalerror.h

Header files should not generally need to include fatalerror.h, and
quite a few source files were not declaring their dependency on it
because some widely-used header files were including it.

Removed unused modulo functionality from vec.h

Moved divide_err functionality to the one place it is used

The matrix-inversion code that calls gmx_fatal was in vec.h so that it
can be inlined, but it's only called every MD step for box inversions,
and never called by mdrun on a per-atom basis, so the need for
inlining is low. The remaining use of FARGS (and thus need for
fatalerror.h) in that code could be removed by throwing an exception
(in some later change). Maybe then it could be put back into a header
for inlining.

Change-Id: I74d7dc6d4568c5d7fd9086ee1d48e54d18267b9d