LibFM provides file management functions built on top of Glib/GIO, 
giving a convenient higher-level API.

vala is an optional dependency (for custom file manager actions).

you can choose between which version of gtk the library will build
against:

  GTK=2  link with gtk+2 (default)
  GTK=3  link with gtk+3
  GTK=0  don't link against gtk at all

pass the script the parameter you prefer, like

  GTK=3 ./libfm.SlackBuild
