Update version macros to retain underscore versions.

CMakeLists.txt

@@ -262,7 +262,7 @@ if (GIT_FOUND)
       OUTPUT_STRIP_TRAILING_WHITESPACE)
   if (${MLPACK_TMP_REV_INFO_RESULT} EQUAL 0)
     set (USING_GIT "YES")
-    add_definitions(-D__MLPACK_GIT_VERSION)
+    add_definitions(-DMLPACK_GIT_VERSION)
     include(CMake/CreateGitVersionHeader.cmake)
 
     add_custom_target(mlpack_gitversion ALL

src/mlpack/core/util/version.hpp

@@ -15,6 +15,12 @@
 #define MLPACK_VERSION_MINOR 0
 #define MLPACK_VERSION_PATCH "x"
 
+// Reverse compatibility; these macros will be removed in future versions of
+// mlpack (3.0.0 and newer)!
+#define __MLPACK_VERSION_MAJOR 2
+#define __MLPACK_VERSION_MINOR 0
+#define __MLPACK_VERSION_PATCH "x"
+
 // The name of the version (for use by --version).
 namespace mlpack {
 namespace util {