Add support for doxygen:alias feature

This allows to replace non-standard Doxygen commands with some (fixed) text
instead of just ignoring them, as was already possible with the feature
doxygen:ignore.

Examples/test-suite/java/doxygen_alias_runme.java

@@ -0,0 +1,32 @@
+
+import doxygen_alias.*;
+import com.sun.javadoc.*;
+import java.util.HashMap;
+
+public class doxygen_alias_runme {
+  static {
+    try {
+      System.loadLibrary("doxygen_alias");
+    } catch (UnsatisfiedLinkError e) {
+      System.err.println("Native code library failed to load. See the chapter on Dynamic Linking Problems in the SWIG Java documentation for help.\n" + e);
+      System.exit(1);
+    }
+  }
+
+  public static void main(String argv[])
+  {
+    CommentParser parser = new CommentParser();
+    com.sun.tools.javadoc.Main.execute("doxygen_alias runtime test",
+                                       "CommentParser",
+                                       new String[]{"-quiet", "doxygen_alias"});
+
+    HashMap<String, String> wantedComments = new HashMap<String, String>();
+    wantedComments.put("doxygen_alias.doxygen_alias.make_something()",
+      "     A function returning something.<br>\n" +
+      " <br>\n" +
+      "     @return A new object which may be null.\n" +
+      "");
+
+    System.exit(parser.check(wantedComments));
+  }
+}