Avoid a 32 kB file allocation on every bitBucketFilePutter.Put
Avoid a 32 kB file allocation on every bitBucketFilePutter.Put

io.Copy usually allocates a 32kB buffer, and due to the large
number of files processed by tar-split, this shows up in Go profiles
as a very large alloc_space total.

It doesn't seem to actually be a measurable problem in any way,
but we can allocate the buffer only once per tar-split creation,
at no additional cost to existing allocations, so let's do so,
and remove the distraction.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

vbatts/tar-split