prettifies code (space formatting in a slightly more consistent way)
some more code formatting; adds additional gpu wrapper functions
adds preprocessor function GPU_ERROR_CHECKING for ENABLE_VERY_SLOW_ERROR_CHECKING
adds GPU support for UNDO_ATTENUATION
Merge branch 'devel' of https://github.com/geodynamics/specfem3d_globe into devel
removes trailing spaces
Merge branch 'devel' of https://github.com/geodynamics/specfem3d_globe into devel