In the event of a multi-line comment, e.g.:
/* for (i = 0; i < 10; ++i)
... deleting the opening /* in C/C++ will result in the trailing */ being highlighted in red as an error. d.vim should similarly colour trailing comment end-marks (currently it just leaves them uncoloured).
The fix should also apply to /+ ... +/ comment blocks.
/+ ... +/
Highlight trailing comment as error