Grammar error messages 2/3: Improve the infinite loop message

New wording is more explanatory.

Part of #371.

lib/compiler/passes/report-infinite-loops.js

@@ -12,13 +12,19 @@ function reportInfiniteLoops(ast) {
   var check = visitor.build({
     zero_or_more: function(node) {
       if (!asts.alwaysConsumesOnSuccess(ast, node.expression)) {
-        throw new GrammarError("Possible infinite loop detected.", node.location);
+        throw new GrammarError(
+          "Possible infinite loop when parsing (repetition used with with an expression that may not consume any input).",
+          node.location
+        );
       }
     },
 
     one_or_more: function(node) {
       if (!asts.alwaysConsumesOnSuccess(ast, node.expression)) {
-        throw new GrammarError("Possible infinite loop detected.", node.location);
+        throw new GrammarError(
+          "Possible infinite loop when parsing (repetition used with with an expression that may not consume any input).",
+          node.location
+        );
       }
     }
   });

spec/unit/compiler/passes/report-infinite-loops.spec.js

@@ -7,7 +7,7 @@ describe("compiler pass |reportInfiniteLoops|", function() {
 
   it("reports infinite loops for zero_or_more", function() {
     expect(pass).toReportError('start = ("")*', {
-      message:  "Possible infinite loop detected.",
+      message:  "Possible infinite loop when parsing (repetition used with with an expression that may not consume any input).",
       location: {
         start: { offset:  8, line: 1, column:  9 },
         end:   { offset: 13, line: 1, column: 14 }
@@ -17,7 +17,7 @@ describe("compiler pass |reportInfiniteLoops|", function() {
 
   it("reports infinite loops for one_or_more", function() {
     expect(pass).toReportError('start = ("")+', {
-      message:  "Possible infinite loop detected.",
+      message:  "Possible infinite loop when parsing (repetition used with with an expression that may not consume any input).",
       location: {
         start: { offset:  8, line: 1, column:  9 },
         end:   { offset: 13, line: 1, column: 14 }