Enable FUSE_CAP_BIG_WRITES in fusepy

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What steps will reproduce the problem?
I use fedora 17 and checked out that the fuse mounted fileobject only got 4096 
Bytes at once per write action. My Filesystem has a Blocksize of 1MB, so the 
small Blocksize is slowing down the speed to 200kB/sec max.

What is the expected output? What do you see instead?
On Windows I get a speed of 2MB/sec, i dont know if thats the reason of write 
size. I'll check it out.

What version of the product are you using? On what operating system?
newest cvn

Please provide any additional information below.
I found already someoune who implemented it, but I didnt get it running on my 
own.

https://bitbucket.org/eug48/id3-split-fuse/commits/28861976048e2810198959521226d
5524b5d55dc

Original issue reported on code.google.com by [email protected] on 20 Feb 2013 at 2:55