Patch from Gerrit: 04_hostlist__hostrange_numstr.diff

hostrange_numstr(): overflow cases

This checks hostrange_numstr() for overflow cases:		    
 * requires n > dims (if dims=1, min 1 digit, else dim + '\0' digits);
   - this precondition simplifies many subsequent checks and
   - addresses if (len == n) then len++ means buf[len] = buf[n];
 * also checks return value of the snprintfs.