lang, engine: Add a metaparam for catching accidental dollar signs

Let's make our life easier for users!

lang/interpret_test/TestAstFunc1/resdupefields0.txtar

@@ -14,6 +14,7 @@ test "test" {
 		sema => ["foo:1", "bar:3",],
 		rewatch => false,
 		realize => true,
+		dollar => false,
 		reverse => true,
 		autoedge => true,
 		autogroup => true,

lang/interpret_test/TestAstFunc1/resdupefields5.txtar

@@ -14,6 +14,7 @@ test "test" {
 		sema => ["foo:1", "bar:3",],
 		rewatch => false,
 		realize => true,
+		dollar => false,
 		reverse => true,
 		autoedge => true,
 		autogroup => true,
@@ -31,6 +32,7 @@ Edge: const -> composite # autoedge
 Edge: const -> composite # autogroup
 Edge: const -> composite # burst
 Edge: const -> composite # delay
+Edge: const -> composite # dollar
 Edge: const -> composite # limit
 Edge: const -> composite # noop
 Edge: const -> composite # poll
@@ -60,3 +62,4 @@ Vertex: const
 Vertex: const
 Vertex: const
 Vertex: const
+Vertex: const

lang/interpret_test/TestAstFunc2/res4.txtar

@@ -14,6 +14,7 @@ test "t1" {
 	#	sema => ["foo:1", "bar:3",],
 	#	rewatch => false,
 	#	realize => true,
+	#	dollar => false,
 	#	reverse => true,
 	#	autoedge => true,
 	#	autogroup => true,
@@ -29,6 +30,7 @@ test "t1" {
 	Meta:sema => ["foo:1", "bar:3",],
 	Meta:rewatch => false,
 	Meta:realize => true,
+	Meta:dollar => false,
 	Meta:reverse => true,
 	Meta:autoedge => true,
 	Meta:autogroup => true,

lang/interpret_test/TestAstFunc3/dollar1.txtar

@@ -0,0 +1,5 @@
+-- main.mcl --
+$foo = "/tmp/file1"
+test "$foo" {}	# catch simple typos! should be "${foo}"
+-- OUTPUT --
+# err: errValidate: test[$foo] did not Validate: the Res name starts with a $

lang/interpret_test/TestAstFunc3/dollar2.txtar

@@ -0,0 +1,7 @@
+-- main.mcl --
+$foo = "/tmp/file1"
+test "$foo" {
+	Meta:dollar => true, # allow what would normally be a typo!
+}
+-- OUTPUT --
+Vertex: test[$foo]