Respect crlf attribute in "git add" even if core.autocrlf has not been set

Respect crlf attribute in "git add" even if core.autocrlf has not been set

When a file's crlf attribute is explicitely set, it does not make sense
to ignore it when adding the file, just because the config variable
core.autocrlf has not been set.

The alternative would be risking to get CR/LF files into the repository
just because one user forgot to set core.autocrlf.

This patch does not affect the case when the crlf attribute is unset,
or when checking files out.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>