Feature request: nona GPU fallback

[Hans Bull]

Since some card drivers do not support the fantastic nona GPU feature, would it be possible to implement a (trivial) fallback to CPU calculation in the case of errors like the one below? CPU fallback is already used when the projection is not supported

Cheers

HB

nona -g  -z LZW -r ldr -m TIFF_m -o _DSC2464-_DSC2466 -i 0 /tmp/huginpto_4gGz3v

nona: using graphics card: Intel Open Source Technology Center Mesa DRI Intel(R) Sandybridge Mobile 

nona: Unsupported framebuffer format in: /build/buildd/hugin-2014.0.0~rc4+dfsg/src/hugin_base/vigra_ext/ImageTransformsGPU.cpp:738

make: *** [_DSC2464-_DSC24660000.tif] error 1