S3Boto3Storage: fix for file-like objects without name, multipart upload support

[pacahon]

In fact, it's partially solves problem. If we pass subclass of File class and forgot override __bool__ method - an error based on empty name still can occur.

[linuxlewis]

👍 on seeing the SHA error. We've worked around it by ensuring we pass a django.core.files.base.File object with name defined.

[pacahon]

@linuxlewis Hi, can you show me where it's already fixed?
UPD. Did you talk about django-storages internals btw?

[linuxlewis]

@pacahon The "fix" is just a workaround in our code. We do something like this...

from cStringIO import StringIO

from django.core.files.storage import default_storage
from django.core.files.base import File

default_storage.save('filename.txt', File(StringIO('content'), name='filename.txt'))

[pacahon]

@linuxlewis Thanks, that was my first thought. But Storage class accepts any file-object, so I'm looking for solution. Of course, my PR in its current state is just another workaround.

[codecov-io]

Codecov Report

Merging #195 into master will increase coverage by 0.53%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
+ Coverage   59.32%   59.85%   +0.53%     
==========================================
  Files          17       17              
  Lines        1694     1684      -10     
==========================================
+ Hits         1005     1008       +3     
+ Misses        689      676      -13

Impacted Files	Coverage Δ
storages/backends/s3boto3.py	82.24% <100%> (+0.51%)	✅
storages/backends/hashpath.py	84.61% <ø> (-1.1%)	❌
storages/backends/s3boto.py	86.09% <ø> (-0.05%)	❌
storages/backends/overwrite.py	0% <ø> (ø)	✅
storages/backends/mogile.py	0% <ø> (ø)	✅
storages/backends/image.py	0% <ø> (ø)	✅
storages/backends/couchdb.py	0% <ø> (ø)	✅
storages/backends/symlinkorcopy.py	0% <ø> (ø)	✅
storages/backends/database.py	0% <ø> (ø)	✅
... and 1 more

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[pacahon]

Should check if already was documented that upload_fileobj waits for bytes or seekable file object in binary mode (the same as old put method)

[jleclanche]

PR needs rebasing but looks good to merge. @jschneier

[jschneier]

Updated and will be applied in #368. Thanks for the report and patch. Apologies for the delay.