Add support for running X setup commands at slim startup

This patch adds support similar to that which can be achieved
in other DM's (such as XDM) by customizing or editing their
Xsetup scripts.  This was added in particular to support
nvidia-drivers based Optimus setups, which need to execute
two xrandr commands in order for Xorg to render on-screen
correctly.  Usage is simple: write a script with the needed
commands, ensure it is executable, and set the xsetup_script
option in slim.conf to the full path of this script.

app.cpp

@@ -295,6 +295,19 @@ void App::Run() {
 
         CreateServerAuth();
         StartServer();
+
+
+        // Run setup script
+        if (cfg->getOption("xsetup_script") != "") {
+            const char* xsetup_cmd = cfg->getOption("xsetup_script").c_str();
+            logStream << APPNAME << ": executing xsetup script '" << xsetup_cmd << "'" << endl;
+            char *tmp = new char[strlen(xsetup_cmd) + 60];
+            sprintf(tmp, xsetup_cmd);
+            system(tmp);
+            delete [] tmp;
+            logStream << APPNAME << ": xsetup script '" << xsetup_cmd << "' finished." << endl;
+        }
+
 #endif
 
     }

cfg.cpp

@@ -41,6 +41,7 @@ Cfg::Cfg()
     options.insert(option("suspend_cmd",""));
     options.insert(option("sessionstart_cmd",""));
     options.insert(option("sessionstop_cmd",""));
+    options.insert(option("xsetup_script",""));
     options.insert(option("console_cmd","/usr/bin/xterm -C -fg white -bg black +sb -g %dx%d+%d+%d -fn %dx%d -T ""Console login"" -e /bin/sh -c ""/bin/cat /etc/issue; exec /bin/login"""));
     options.insert(option("screenshot_cmd","import -window root /slim.png"));
     options.insert(option("welcome_msg","Welcome to %host"));

slim.conf

@@ -16,6 +16,11 @@ xauth_path         /usr/bin/xauth
 # Xauth file for server
 authfile           /var/run/slim.auth
 
+# Optional script for X setup - to run commands after
+# X starts but before the panels draw. This provides
+# the ability to add custom commands, the same as one
+# would by modifying the Xsetup_0 script in XDM.
+#xsetup_script      /etc/X11/Xsetup_0.sh
 
 # Activate numlock when slim starts. Valid values: on|off
 # numlock             on