Allow generate default-preset tool to generate preset for given plugname only.

[brummer10]

Hi
While working on deploying some plugs on the MOD, this little tool is very useful. Just, I prefer to generate the default-preset.ttl file only for the plug I'm working on, instead regenerate it for the complete folder I'm working in. The attached patch add this functionality to generate-default.cpp
This is dune with respect the previous behave, so new usage with this patch will be
usage: generate <lv2-folder> [lv2-plugnamer]
were lv2-plugname is optional.

diff --git a/generate-default-preset/generate.cpp b/generate-default-preset/generate.cpp
index 9215a9a..80a3f11 100644
--- a/generate-default-preset/generate.cpp
+++ b/generate-default-preset/generate.cpp
@@ -388,11 +388,12 @@ int main(int argc, char* argv[])
 {
     if (argc < 2)
     {
-        fprintf(stdout, "usage: %s <lv2-folder>\n", argv[0]);
+        fprintf(stdout, "usage: %s <lv2-folder>  [lv2-plugnamer]\n", argv[0]);
         return 1;
     }
 
     char* lv2_folder = argv[1];
+    char* lv2_plug = argv[2];
 
 #if 0
     stat(s);
@@ -415,11 +416,26 @@ int main(int argc, char* argv[])
 
     const LilvPlugins* const plugins = lilv_world_get_all_plugins(world);
 
-    LILV_FOREACH(plugins, iter, plugins)
+    if (lv2_plug != 0) {
+        LILV_FOREACH(plugins, iter, plugins)
+        {
+            const LilvPlugin* plugin = lilv_plugins_get(plugins, iter);
+            if (plugin)
+            {
+                if (strcmp(lilv_node_as_string(lilv_plugin_get_name(plugin)),lv2_plug) ==0)
+                {
+                    create_plugin_preset(world, plugin);
+                }
+            }
+        }
+    }
+    else
     {
-        create_plugin_preset(world, lilv_plugins_get(plugins, iter));
+        LILV_FOREACH(plugins, iter, plugins)
+        {
+            create_plugin_preset(world, lilv_plugins_get(plugins, iter));
+        }
     }
-
     lilv_world_free(world);
     free(lv2_folder);