expand_files() cleanup: Make expand_files() common code for
fork.c:fork/copy_files(), open.c:open/get_unused_fd() and
fcntl.c:dup/locate_fd().

expand_files() does both expand_fd_array and expand_fd_set based on the
need.  This is used in dup().  open() and fork() duplicates the work of
expand files.  At all places we check for expanding fd array, we also check
for expanding fdset.  There is no need of checking and calling them
seperately.

This change also moves the expand_files to file.c from fcntl.c, and makes
the expand_fd_array and expand_fd_set local to that file.
Signed-off-by: Prasanna Meda <pmeda@akamai.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>