rsync "Error opening file" exception when filename or directory has a + (plus sign) in it

My rsync command fails with:

`"CommandException: Error opening file "file:///Volumes/Drive/Docs/1 1.doc": [Errno 2] No such file or directory: u'/Volumes/Drive/Docs/1 1.doc'"`

The actual filename of the file referred to in the exception is:
`/Volumes/Drive/Docs/1 + 1.doc`

Here's the exact command I'm running:
`gsutil -m rsync -d -r /Volumes/Drive/ gs://my-bucket/`

It looks like the plus sign is being substituted with a space character whenever gsutil builds its sync list. My guess is that this has something to do with the fact that the plus sign is a special character in regex?

I would be happy to put together a PR and test if someone could at least point me in the general right direction in the code. My guess is that it's sub

Start by reproducing the reported gsutil -m rsync command with a filename containing a plus sign, then trace how the local sync list is built. Done means the plus sign remains part of the filename and the rsync operation completes without the file-opening exception.

Written by the indexing model from the issue text.