Include SDL information in system info text.

Adds bpy.app.sdl to expose SDL version information.

When SDL is not available on a Linux system, certain Blender features
are silently disabled (like joystick support in the BGE). This change
is the first step towards making it more obvious why something isn't
working.

SDL information is exposed to Python via bpy.app.sdl, in the same way
as OCIO and OIIO information is exposed.

Generated system-info.txt contains SDL loading method (linked or
dynamically loaded by Blender) and SDL version number.

Reviewed by: sergey, campbellbarton

Differential Revision: https://developer.blender.org/D1112

source/blender/python/intern/bpy_app.c

@@ -36,6 +36,7 @@
 #include "bpy_app_ffmpeg.h"
 #include "bpy_app_ocio.h"
 #include "bpy_app_oiio.h"
+#include "bpy_app_sdl.h"
 #include "bpy_app_build_options.h"
 
 #include "bpy_app_translations.h"
@@ -97,6 +98,7 @@ static PyStructSequence_Field app_info_fields[] = {
 	{(char *)"ffmpeg", (char *)"FFmpeg library information backend"},
 	{(char *)"ocio", (char *)"OpenColorIO library information backend"},
 	{(char *)"oiio", (char *)"OpenImageIO library information backend"},
+	{(char *)"sdl", (char *)"SDL library information backend"},
 	{(char *)"build_options", (char *)"A set containing most important enabled optional build features"},
 	{(char *)"handlers", (char *)"Application handler callbacks"},
 	{(char *)"translations", (char *)"Application and addons internationalization API"},
@@ -173,6 +175,7 @@ static PyObject *make_app_info(void)
 	SetObjItem(BPY_app_ffmpeg_struct());
 	SetObjItem(BPY_app_ocio_struct());
 	SetObjItem(BPY_app_oiio_struct());
+	SetObjItem(BPY_app_sdl_struct());
 	SetObjItem(BPY_app_build_options_struct());
 	SetObjItem(BPY_app_handlers_struct());
 	SetObjItem(BPY_app_translations_struct());