Added sanity test of TIMEFN

This commit adds a sanity check of the test script TIMEFN, which is by
default 'time -p', for the scripts that define it. The scripts are
currently written such that if there is no 'time' executable, such as in
Debian 9, then some of the scripts fail and some don't but should. This
commit fixes that problem.

test/test_perf_state.sh

@@ -20,6 +20,7 @@ fin=$dir/fin
 
 # time function (this is a mess to get right on freebsd/linux)
 : ${TIMEFN:=time -p} # portability: 2>&1 | awk '/real/ {print $2}'
+if ! $TIMEFN true; then err "A working time function" "'$TIMEFN' does not work"; fi
 
 APPNAME=example