clean up max_line_len

- never exceed specified limit
- otherwise warning is shown
- enabled only for final output

closes #1496

test/compress/max_line_len.js

@@ -0,0 +1,28 @@
+too_short: {
+    beautify = {
+        max_line_len: 10,
+    }
+    input: {
+        function f(a) {
+            return { c: 42, d: a(), e: "foo"};
+        }
+    }
+    expect_exact: 'function f(a){\nreturn{\nc:42,\nd:a(),\ne:"foo"}}'
+    expect_warnings: [
+        "WARN: Output exceeds 10 characters"
+    ]
+}
+
+just_enough: {
+    beautify = {
+        max_line_len: 14,
+    }
+    input: {
+        function f(a) {
+            return { c: 42, d: a(), e: "foo"};
+        }
+    }
+    expect_exact: 'function f(a){\nreturn{c:42,\nd:a(),e:"foo"}\n}'
+    expect_warnings: [
+    ]
+}