Replace calls to xmessage to batt-low.sh so that message is only 
shown once.

We only patch main.c and not main.vala so makefile doesn't trigger
vala -> C compilation.

diff -ur vattery-0.7.5/src/main.c vattery-0.7.5-new/src/main.c
--- vattery-0.7.5/src/main.c	2012-06-17 22:25:05.000000000 +0700
+++ vattery-0.7.5-new/src/main.c	2015-12-26 01:42:03.730550571 +0700
@@ -383,12 +383,12 @@
 	_tmp11_ = g_strdup ("5");
 	_g_free0 (self->priv->percent_critical);
 	self->priv->percent_critical = _tmp11_;
-	_tmp12_ = _ ("battery is very low");
-	_tmp13_ = g_strconcat ("xmessage ", _tmp12_, NULL);
+	_tmp12_ = _ ("low");
+	_tmp13_ = g_strconcat ("batt-low.sh ", _tmp12_, NULL);
 	_g_free0 (self->priv->command_warning);
 	self->priv->command_warning = _tmp13_;
-	_tmp14_ = _ ("battery is critically low");
-	_tmp15_ = g_strconcat ("xmessage ", _tmp14_, NULL);
+	_tmp14_ = _ ("critical");
+	_tmp15_ = g_strconcat ("batt-low.sh ", _tmp14_, NULL);
 	_g_free0 (self->priv->command_critical);
 	self->priv->command_critical = _tmp15_;
 	_tmp16_ = g_get_user_config_dir ();