I made a lots of changes, mainly code cleaning. Links in first post.
Now it doesn't try to patch to native resolution, but turns VESA modes to fit aspect for everyone, including ATI and Intel. It doesn't patch the full modeline for anyone, just the horizontal active and vertical active (with minus one values for NVIDIA). So Id' like to know if it still works for NVIDIA, it shouldn't make a lot of changes for ATI.
Also it doesn't patch modes equal or below 800x600, and corrects the 1400 and 1600 resolution to 1440 and 1680 respectively.
I moved the "reapply" code out from ExecKernel and back to bootcommon, and rearanged it, should be safer. It was likely to produce errors (I hope there is no more hanging, ati.c is untouched).
Most importantly, for coders:
I renamed the file from 915resolution.c/.h to autoresolution.c/.h because it didn't make sense anymore.
I moved vendor specific code to files named accordingly: ati_resolution.c/.h nvidia_resolution.c/.h and gma_resolution.c/.h
I removed lots of little remaining parts of various and vain older trials.
The getMode function is gone, it's not used any more. cvt calculation is still there, just in case, but will probably be removed.
The useless stuff in gui.c has been removed.
I still have to merge shortatombios.h to ati_resolution.h, there is no reason to have two headers when others have one.
It won't change lots of stuff but it was beginning to be a real mess, particularly in open_vbios, where code for ATI and NVidia were mixed with code for Intel GMA. Now there is a different function for each of them, in their respective files, the same for set_mode (now patch_vbios, more accurate). The patch_vbios function is rearranged to avoid duplicate code (there is still some). The patch procedure is the same for ATI and Intel, NVidia differs because of the two tables.
It is a bit easier to read (at least, it is for me).
Voilà! I hope it is still working for every one, and that coders will appreciate to know when they're reading code for ATI, Intel, Nvidia or all of them.
P.S. @ Azimutz and diebuche, could you post a diff against my sources so I can upload a better precompiled booter? I attached the whole thing.