Update version.c to 7.4.455
vim-patch:7.4.455

Problem:  Completion for :buf does not use 'wildignorecase'.
          (Akshay H)

Solution: Pass the 'wildignorecase' flag around.

https://code.google.com/p/vim/source/detail?r=ebc72764fa1e74758ae1ef9d3f49301f80fc3aa4