mailinfo: don't require "text" mime type for attachments

mailinfo: don't require "text" mime type for attachments

Currently "git am" does insane things if the mbox it is given contains
attachments with a MIME type that aren't "text/*".

In particular, it will still decode them, and pass them "one line at a
time" to the mail body filter, but because it has determined that they
aren't text (without actually looking at the contents, just at the mime
type) the "line" will be the encoding line (eg 'base64') rather than a
line of *content*.

Which then will cause the text filtering to fail, because we won't
correctly notice when the attachment text switches from the commit message
to the actual patch. Resulting in a patch failure, even if patch may be a
perfectly well-formed attachment, it's just that the message type may be
(for example) "application/octet-stream" instead of "text/plain".

Just remove all the bogus games with the message_type. The only difference
that code creates is how the data is passed to the filter function
(chunked per-pred-code line or per post-decode line), and that difference
is *wrong*, since chunking things per pre-decode line can never be a
sensible operation, and cannot possibly matter for binary data anyway.

This code goes all the way back to March of 2007, in commit 87ab79923463
("builtin-mailinfo.c infrastrcture changes"), and apparently Don used to
pass random mbox contents to git. However, the pre-decode vs post-decode
logic really shouldn't matter even for that case, and more importantly, "I
fed git am crap" is not a valid reason to break *real* patch attachments.

If somebody really cares, and determines that some attachment is binary
data (by looking at the data, not the MIME-type), the whole attachment
should be dismissed, rather than fed in random-sized chunks to
"handle_filter()".

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Don Zickus <dzickus@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>