Update version.c to 7.4.457
vim-patch:7.4.457

Problem:  Using getchar() in an expression mapping may result in
          K_CURSORHOLD, which can't be recognized.

Solution: Add the <CursorHold> key.  (Hirohito Higashi)

https://code.google.com/p/vim/source/detail?r=96761b6789f61a8dee1551b7cea98e669fb90fb3