randltl: accept a number of atomic propositions

Suggested by Joachim Klein.

* src/bin/randltl.cc: Implement it.
* src/ltltest/rand.test: Test it.
* doc/org/randltl.org, NEWS: Document it.

src/ltltest/rand.test

@@ -97,3 +97,29 @@ c
 EOF
 
 diff expected out2
+
+
+# atomic proposition can be implicitly specified using a number
+$randltl -n 1000 3 --tree-size=10..20 > out
+grep -q p0 out
+grep -q p1 out
+grep -q p2 out
+grep p3 out && exit 1
+
+
+# We should be able to generate exactly two formulas with 0 atomic
+# propositions.
+run 0 $randltl -n2 0 | sort > out
+cat >expected <<EOF
+0
+1
+EOF
+diff out expected
+
+# requesting more formulas should fail
+run 2 $randltl -n3 0
+
+# If more numbers are given, there are interpreted as atomic propositions
+run 0 $randltl -n1000 0 1 > out
+grep -q '"0"' out
+grep -q '"1"' out