Adding the optional ability to set the size of each file read when DYNAM...

...IC_FILE_UPLOAD is being used.

When I do large file uploads with $DYNAMIC_FILE_UPLOAD it's hard coded to read the file in 2048 byte chunks. I find that this makes for some very slow transfers. As a test I went in and modified to to send 64k chunks and the transfer was much faster.

I'm proposing a possible solution to allow the user to set the amount of bytes they want to read at a time from the file. I'm open to discussion or implementing other ways but this seems like it fits with the interface.