autofile: don't copy CAutoFile by value
autofile: Disallow by-value copies of CAutoFile

One might assume that CAutoFile would be ref-counted so that a copied object
would delay closing the underlying file until all copies have gone out of
scope. Since that's not the case with CAutoFile, explicitly disable copying.
Merge pull request #4986

6eb67b0 autofile: Disallow by-value copies of CAutoFile (Cory Fields)
eee030f autofile: don't copy CAutoFile by value (Cory Fields)