Detect recursive WAITs

Recursive waits cause subtle problems that are hard to trouble shoot.
Throw an error to make it evident.

src/boot/errors.r

@@ -119,6 +119,8 @@ Script: [
 	parse-command:      [{PARSE - command cannot be used as variable:} :arg1]
 	parse-series:       [{PARSE - input must be a series:} :arg1]
 
+	recursive-wait: 	{recursive calls to WAIT}
+
 ;   bad-prompt:         [{Error executing prompt block}]
 ;   bad-port-action:    [{Cannot use} :arg1 {on this type port}]
 ;   face-error:         [{Invalid graphics face object}]

src/core/n-io.c

@@ -31,6 +31,8 @@
 
 //#define HELPER
 
+static int waited = 0; //for recursive WAIT detection
+
 
 /** Helper Functions **************************************************/
 
@@ -309,7 +311,6 @@ static REBSER *Read_All_File(char *fname)
 }
 #endif
 
-
 /***********************************************************************
 **
 */	REBNATIVE(wait)
@@ -321,6 +322,12 @@ static REBSER *Read_All_File(char *fname)
 	REBSER *ports = 0;
 	REBINT n = 0;
 
+	if (waited != 0) {
+		Trap0(RE_RECURSIVE_WAIT);
+	}
+
+	++ waited;
+
 	SET_NONE(D_RET);
 
 	if (IS_BLOCK(val)) {
@@ -332,7 +339,10 @@ static REBSER *Read_All_File(char *fname)
 			if (IS_INTEGER(val) || IS_DECIMAL(val)) break;
 		}
 		if (IS_END(val)) {
-			if (n == 0) return R_NONE; // has no pending ports!
+			if (n == 0) { // has no pending ports!
+			   --waited;
+			   return R_NONE;
+			}
 			// SET_NONE(val); // no timeout -- BUG: unterminated block in GC
 		}
 	}
@@ -353,7 +363,10 @@ static REBSER *Read_All_File(char *fname)
 		break;
 
 	case REB_PORT:
-		if (!Pending_Port(val)) return R_NONE;
+		if (!Pending_Port(val)) {
+			-- waited;
+			return R_NONE;
+		}
 		ports = Make_Block(1);
 		Append_Val(ports, val);
 		// fall thru...
@@ -373,9 +386,13 @@ static REBSER *Read_All_File(char *fname)
 	// Process port events [stack-move]:
 	if (!Wait_Ports(ports, timeout)) {
 		Sieve_Ports(NULL); /* just reset the waked list */
+		-- waited;
+		return R_NONE;
+	}
+	if (!ports) {
+		-- waited;
 		return R_NONE;
 	}
-	if (!ports) return R_NONE;
 	DS_RELOAD(ds);
 
 	// Determine what port(s) waked us:
@@ -387,6 +404,8 @@ static REBSER *Read_All_File(char *fname)
 		else SET_NONE(D_RET);
 	}
 
+	-- waited;
+
 	return R_RET;
 }