bookmarks: forbid \0 \r \n : in bookmark names (BC) We restrict : to 1. make it easer to convert bookmarks to git branches, 2. use : later for a syntax to push a local bookmark to a remote bookmark of a different name. \0, \n, \r are fobbidden they are used to separate bookmarks in the bookmark file. This change breaks backward compatbility as ':' was an allowed character in previous versions.