cuda: modifier in function definations
cuda: dllapi lower case
cuda: avoid symbol name conflicting
cuda: keep the original cuda headers from nvidia and let them work with
my dllapi project

use namespace to avoid symbol conflict
why use dllapi? because we can use any version of cuda api easily. Other
projects such as lavfilters can only use cuda 3.1 api now
Merge branch 'master' into cuda-dll

Conflicts:
	src/cuda/helper_cuda.h
	src/libQtAV.pro
cuda: support dllapi, or use cuda_api class, or link against cuda

dllapi submodule not added yet