vim-patch: 7.4.344

Problem:    Unnecessary initializations and other things related to
	    matchaddpos().
Solution:   Code cleanup. (Alexey Radkov)

NOTE: The original patch modified the logic for the for loop in
window.c:5257, but this caused troubles, so those changes aren't
included here (see the comments on
https://github.com/neovim/neovim/pull/1107#issuecomment-54053808).