Check for recipe line count overflow before it overflows

Check for recipe line count overflow before it overflows

awk 'BEGIN {
       print "x:"
       for (i = 0; i < 65536; i++)
         printf "\techo %d\n", i}
    ' | make -f -

Outputs only "make: 'x' is up to date."  Larger values run only the
lines above 65536.  Reported by Paul Eggert <eggert@cs.ucla.edu>.

* src/commands.c (chop_commands): Check the line count before it has
a chance to overflow.  Use size_t for max count so it can't overflow.
Remove stray 'd' in diagnostic.