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/common.mk

@@ -583,6 +583,7 @@ $(eval HAS_DOXYGEN := $($(LANGUAGE)_HAS_DOXYGEN))
 ifdef HAS_DOXYGEN
 DOXYGEN_TEST_CASES += \
 	doxygen_parsing \
+	doxygen_alias \
 	doxygen_ignore \
 	doxygen_basic_translate \
 	doxygen_basic_notranslate \

Examples/test-suite/doxygen_alias.i

@@ -0,0 +1,22 @@
+%module doxygen_alias
+
+#ifdef SWIGJAVA
+%feature("doxygen:alias:nullptr") "null"
+#elif defined(SWIGPYTHON)
+%feature("doxygen:alias:nullptr") "None"
+#else
+%feature("doxygen:alias:nullptr") "NULL"
+#endif
+
+%inline %{
+
+class Something {};
+
+/**
+    A function returning something.
+
+    @returns A new object which may be @nullptr.
+ */
+Something* make_something() { return 0; }
+
+%}

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));
+  }
+}

Examples/test-suite/python/doxygen_alias_runme.py

@@ -0,0 +1,12 @@
+#!/usr/bin/python
+
+import doxygen_alias
+import inspect
+import commentVerifier
+
+commentVerifier.check(inspect.getdoc(doxygen_alias.make_something),
+    """\
+A function returning something.
+
+:rtype: :py:class:`Something`
+:return: A new object which may be None.""")