Add per-repository eol normalization

Add per-repository eol normalization

Change the semantics of the "crlf" attribute so that it enables
end-of-line normalization when it is set, regardless of "core.autocrlf".

Add a new setting for "crlf": "auto", which enables end-of-line
conversion but does not override the automatic text file detection.

Add a new attribute "eol" with possible values "crlf" and "lf".  When
set, this attribute enables normalization and forces git to use CRLF or
LF line endings in the working directory, respectively.

The line ending style to be used for normalized text files in the
working directory is set using "core.autocrlf".  When it is set to
"true", CRLFs are used in the working directory; when set to "input" or
"false", LFs are used.

Signed-off-by: Eyvind Bernhardsen <eyvind.bernhardsen@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>