perf: auto detect seq(1) and jot(1)

makes perf.sh more portable

perf.sh

@@ -3,21 +3,26 @@
 set -eu
 
 num=1000000
+seq=seq
+
+if [ -x /usr/bin/jot ]; then
+	seq=jot
+fi
 
 rm -f perf_*.log
 
-for i in `jot 10`; do
+for i in `$seq 10`; do
 	/usr/bin/time st -e                      jot $num 2>>perf_0.log
 done
 
-for i in `jot 10`; do
+for i in `$seq 10`; do
 	/usr/bin/time st -e ./ptty               jot $num 2>>perf_1.log
 done
 
-for i in `jot 10`; do
+for i in `$seq 10`; do
 	/usr/bin/time st -e ./ptty ./ptty        jot $num 2>>perf_2.log
 done
 
-for i in `jot 10`; do
+for i in `$seq 10`; do
 	/usr/bin/time st -e ./ptty ./ptty ./ptty jot $num 2>>perf_3.log
 done