[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.
I was wrong about `xmallocz`--it doesn't initialize the memory to zero and we don't seem to have an equivalent. As long as all the members get initialized, it shouldn't be an issue.