when a mysql directory is specified in the lib list, tell the linker to add that directory to the compiled library's LD_RUN_PATH

ext/extconf.rb

@@ -130,4 +130,8 @@ end
 
 $CPPFLAGS += " -DRUBY19" if RUBY_VERSION =~ /1.9/
 
-create_makefile("mysql")
+if hard_mysql_path = $libs[%r{-L(/[^ ]+)}, 1]
+	$LDFLAGS << " -Wl,-rpath,#{hard_mysql_path}"
+end
+
+create_makefile("mysql")