Fix exec icon location and bring it into XDG compliance

diff --git a/amarok/src/iconloader.cpp b/amarok/src/iconloader.cpp
index 937b2cf..d0e307e 100644
--- a/amarok/src/iconloader.cpp
+++ b/amarok/src/iconloader.cpp
@@ -52,7 +52,7 @@
         iconMap["edit"]                 = "edit";
         iconMap["edit-copy"]             = "edit-copy";
         iconMap["equalizer"]            = "equalizer";
-        iconMap["external"]             = "exec";
+        iconMap["external"]             = "application-x-executable";
         iconMap["fastforward"]          = "2rightarrow";
         iconMap["favourite_genres"]     = "kfm";
         iconMap["files"]                = "folder";