efl: add eina_file_copy()

efl: add eina_file_copy()

it's useful to copy file from one place to another and this will be
used in eio' s implementation.

NOTE: did not use mmap here as mmap faults may be cumbersome to handle
(Eina_File itself does that, but in a nasty way) and the
implementation would be severely different as there is no Eina_File
from FD, and there is no way to inject custom memory/fd into the
Eina_File's fault handling. The performance would not be that
different anyways and the splice() is already in there for systems
with good performance (read: Linux).

SVN revision: 81942