libsyntax: introduce 'fn is_keyword_ahead(dist, keywords)'.
libsyntax: introduce 'fn is_keyword_ahead(dist, keywords)'.

aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust