add a RUBY_PATCHLEVEL_SUFFIX which can include branch names

Author: Charlie Somerville

version.h

@@ -17,10 +17,16 @@
 # endif
 #endif
 
+#ifdef RUBY_GITHUB_BRANCH
+# define RUBY_PATCHLEVEL_SUFFIX "-github"STRINGIZE(RUBY_GITHUB_VERSION)"-"RUBY_GITHUB_BRANCH
+#else
+# define RUBY_PATCHLEVEL_SUFFIX "-github"STRINGIZE(RUBY_GITHUB_VERSION)
+#endif
+
 #if RUBY_PATCHLEVEL == -1
 #define RUBY_PATCHLEVEL_STR "dev"
 #else
-#define RUBY_PATCHLEVEL_STR "p"STRINGIZE(RUBY_PATCHLEVEL) "-github"STRINGIZE(RUBY_GITHUB_VERSION)
+#define RUBY_PATCHLEVEL_STR "p"STRINGIZE(RUBY_PATCHLEVEL) RUBY_PATCHLEVEL_SUFFIX
 #endif
 
 #ifndef RUBY_REVISION