Attempt to copy a regular file, even if stat says it is empty.

Attempt to copy a regular file, even if stat says it is empty.
* NEWS: Document this bug fix.
* src/copy.c (copy_reg): Read from a regular file, even if it
appears (stat.st_size == 0) to be empty.  This reverts an
optimization introduced on 2005-11-23 for coreutils-6.0.
Otherwise, "cp /proc/cpuinfo /tmp" creates an empty file,
on e.g., linux-2.6.20.
* tests/cp/proc-zero-len: New file.  Test for the above.
* tests/cp/Makefile.am (TESTS): Add proc-zero-len.
Reported by Dan Berrangé.