update figshare uploader to use readexactly()
update figshare uploader to use readexactly()

 * Figshare will time-out without a helpful message if the size of the
   data sent is less than the size expected.

TomBaxter/waterbutler,CenterForOpenScience/waterbutler,Johnetordoff/waterbutler,RCOSDP/waterbutler,rdhyee/waterbutler,felliott/waterbutler