Issue 882: add standard hook to reject text files with CRLF. While the win32text extension does LF <-> CRLF conversion, and will issue a warning in case a file already in the repository uses CRLF, it provides no mechanism for verifying that incoming changes use LF. In a large development team with some Windows users, it is virtually guaranteed that someone will forget to set up the encode filter correctly and accidentally check in a file using CRLF, which can cause warnings for other Windows users when they next fetch changes. Since this is a general problem it is desirable to have a pre-commit (or -push) hook available to reject such accidents earlier rather than trying to fix them up after the fact.