Move general functions out of typedefs.h

- Move overallocation routines to smalloc.h.  Perhaps the DD routines
  could go higher up the dependency stack, but then again, they weren't
  particularly high earlier.
- Move gmx_step_str() to cstringutil.h.  This could probably go away
  completely in favor of GMX_PRId64, but here it will force less
  dependencies on code that still uses it.

These changes allow files that use one of these functions to still get
rid of all unnecessary dependencies that typedefs.h brings.

Change-Id: Ic7973799c14f1748867965fda5bf8e33fae4fd0c