[RFC] Add matchaddpos()-related vim patches. [vim-patch: 7.4.330, 7.4.334, 7.4.343, 7.4.344, 7.4.362]

Adds patches 7.4.330, 334, 344 and 362.
:+1:, defining things in the closest scope possible is good for compilers and humans alike.

Also, for new vim functions, I'd like to propose that we automatically add the attribute `FUNC_ATTR_NONNULL_ALL`, because the vim interpreter makes sure that the arguments cannot be `NULL`. This could help static analyzers (like coverity, possibly also clang).