Fix mozilla components loading when sugar is running from source.

We don't attempt to load components from source, since that would
be insanely complicated.

bin/sugar.in

@@ -1,3 +1,4 @@
+export SUGAR_PREFIX=@prefix@
 export SUGAR_PATH=@prefix@/share/sugar
 export GTK2_RC_FILES=@prefix@/share/sugar/data/sugar-xo.gtkrc
 dbus-launch --exit-with-session sugar-shell

browser/sugar-browser.cpp

@@ -159,13 +159,23 @@ sugar_browser_startup(const char *profile_path, const char *profile_name)
 
     old_handler = XSetErrorHandler(error_handler);
 
+    const char *prefix = g_getenv("SUGAR_PREFIX");
+    if (prefix == NULL) {
+        g_print("The SUGAR_PREFIX environment variable is not set.");
+        exit(1);
+    }
+    
+    char *components_path = g_build_filename(prefix, "share/sugar", NULL);
+
     GeckoDirectoryProvider *dirProvider =
-        new GeckoDirectoryProvider(g_getenv(SUGAR_PATH));
+        new GeckoDirectoryProvider(components_path);
     if (!dirProvider) {
         g_warning ("failed to create GeckoDirectoryProvider");
         return FALSE;
     }
 
+    g_free(components_path);
+
     NS_ADDREF (dirProvider);
 
     nsCOMPtr<nsIDirectoryServiceProvider> dp (do_QueryInterface (dirProvider));

sugar/env.py

@@ -22,7 +22,7 @@ def _get_prefix_path(base, path=None):
     if os.environ.has_key('SUGAR_PREFIX'):
         prefix = os.environ['SUGAR_PREFIX']
     else:
-        prefix = '/usr'
+        raise RuntimeError("The SUGAR_PREFIX environment variable is not set.")
 
     if path:
         return os.path.join(prefix, base, path)