Added HandlerSocket plugin

- Fixed compiler errors
- Modified Makefiles to be part of plugin directory
- Some minor changes in database.cpp to use the new MariaDB handler interface

plugin/handler_socket/perl-Net-HandlerSocket/t/HandlerSocket.t

@@ -0,0 +1,15 @@
+# Before `make install' is performed this script should be runnable with
+# `make test'. After `make install' it should work as `perl HandlerSocket.t'
+
+#########################
+
+# change 'tests => 1' to 'tests => last_test_to_print';
+
+use Test::More tests => 1;
+BEGIN { use_ok('Net::HandlerSocket') };
+
+#########################
+
+# Insert your test code below, the Test::More module is use()ed here so read
+# its man page ( perldoc Test::More ) for help writing this test script.
+