res = f_copy(source, dest)
returns:
0 : no error
-1 : cannot open source
-2 : cannot open dest
-3 : error while writing
-4 : disk full while writing
git-svn-id: http://qeforge.qe-forge.org/svn/q-e/trunk/espresso@10111 c92efa57-630b-4861-b058-cf58834340f0