build, data: the Greek capitals by name; one way to run python3; bench.sh checks its own binary

Δ Γ Λ Ω Φ Ψ Σ Θ answered only to De, Ga, La, Om, Ph, Ps, Si, Th, while
their small letters answered to delta, gamma and the rest; they answer to
the names too now.  mkemoji and cldr2emoji write UTF-8 whatever the
locale, as the other generators already did; verify-map calls python3 the
one way; the tests' include path drops a directory nothing includes
through; and bench.sh says which binary is missing instead of blaming the
daemon ten seconds later.

bench.sh

@@ -9,6 +9,11 @@ if test "$#" -ne 0; then
 	exit 1
 fi
 
+if ! test -x ./bench/bench; then
+	echo "bench.sh: ./bench/bench is not executable; run make bench first" >&2
+	exit 1
+fi
+
 strans_pid=
 perf_pid=