Fixed initializing the haptic system from an XInput joystick
Thanks to Franz Schrober for the fix inspiration.
Fixed warning about unused variable.
Fixed bug: SDL2 Xinput joystick axis jumps from positive to negative

Franz Schrober

Attached is my patch. It ensures that the values are correctly limitted between -32767 and 32767 (otherwise the negator - and the conversion to sint16 would corrupt the result)

I am using Motioninjoy (Dualshock 3 Sixaxxis controller on Windows 7)  together with a recent SDL2 (post rc1) and noticed with the testjoystick binary that the axis 3 (left analog up/down) jumps when going in down direction from 32257 to -32768. This seems obviously wrong and I have never seen this before. In my games the people are now going backwards before they start to sprint forward when the player actually wants to run as fast as possible backwards. This also happens on the axis 2 (right analog stick up/down)

This problem doesn't happen in DX mode
Fixed bug updating the clip rect for the software renderer
Updated testshader for the SDL 2.0 API
We don't want to save the alpha modulation, we want to save the blend mode.