Running kivy_sysprep.sh results in an error: unable to run sdl-config.

[GijsTimmers]

Hello, thank you for this project, it certainly looks very interesting.

When running kivy_sysprep.sh, I'm running into an error:

(...)
Requirement already up-to-date: numpy in /usr/local/lib/python2.7/dist-packages
destination directory: pygame
requesting all changes
adding changesets
adding manifests
adding file changes
added 3405 changesets with 14829 changes to 1790 files (+14 heads)
updating to branch default
673 files updated, 0 files merged, 0 files removed, 0 files unresolved


WARNING, No "Setup" File Exists, Running "config.py"
Using UNIX configuration...


Hunting dependencies...
sh: 1: sdl-config: not found
sh: 1: sdl-config: not found
sh: 1: sdl-config: not found
WARNING: "sdl-config" failed!
sh: 1: smpeg-config: not found
sh: 1: smpeg-config: not found
sh: 1: smpeg-config: not found
WARNING: "smpeg-config" failed!
sh: 1: freetype-config: not found
sh: 1: freetype-config: not found
sh: 1: freetype-config: not found
WARNING: "freetype-config" failed!
Unable to run "sdl-config". Please make sure a development version of SDL is installed.


WARNING, No "Setup" File Exists, Running "config.py"
Using UNIX configuration...


Hunting dependencies...
sh: 1: sdl-config: not found
sh: 1: sdl-config: not found
sh: 1: sdl-config: not found
WARNING: "sdl-config" failed!
sh: 1: smpeg-config: not found
sh: 1: smpeg-config: not found
sh: 1: smpeg-config: not found
WARNING: "smpeg-config" failed!
sh: 1: freetype-config: not found
sh: 1: freetype-config: not found
sh: 1: freetype-config: not found
WARNING: "freetype-config" failed!
Unable to run "sdl-config". Please make sure a development version of SDL is installed.