From: Nipunn Koorapati <nipunn@dropbox.com>

When fetch-pack fails with a bad pack header, the
provided error globs together several distinct error types -
EOF, Bad Signature, and Pack version unsupported.

Provide the more detailed error
to the user so they can debug their situation further.

Before:
protocol error: bad pack header

After:
protocol error: bad pack header: eof before pack header was fully read

Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>

Submitted-As: https://lore.kernel.org/git/pull.755.git.1602762128039.gitgitgadget@gmail.com