Improve Minify_Lines algorithm and add tests

Fixes #531
Fixes #534

tests/_test_files/lines/url.out.js

@@ -0,0 +1,17 @@
+
+/* url.in.js */
+
+/* 1  */ foo; /* http://example.com */
+/* 2  */ bar;
+/* 3  */
+/* 4  */ foo; /*
+/* 5  *|     http://example.com */
+/* 6  */ bar;
+/* 7  */
+/* 8  */ foo = "http://example.com"; /* hello */
+/* 9  */ bar;
+/* 10 */
+/* 11 */ foo = "http://example.com"; /*
+/* 12 *| hello */
+/* 13 */ bar;
+/* 14 */