vimscript's own syntax highlighter ignores line continuations

[GoogleCodeExporter]

What steps will reproduce the problem?
Highlight the following source with vim's own highlighter:
syn keyword foo bar print
syn keyword foo
            \ bar print

What is the expected output? What do you see instead?
Neither "print" should highlighted as they are in a keyword list for syn 
keyword.
The second "print" gets highlighted, I guess because vim.vim doesn't handle the 
line continuation properly.

What version of the product are you using? On what operating system?
vim 7.4.738 on Arch Linux.

Original issue reported on code.google.com by anntzer....@gmail.com on 7 Jul 2015 at 7:27