package.bbclass: fix spurious 'installed but not shipped' warning

For packages that have files installed that aren't in a subdirectory,
the following build WARNING is emitted (this for initramfs-live-boot
as an example):

WARNING: For recipe initramfs-live-boot, the following files were
 installed but not shipped in any package:
WARNING:   init

The problem is that the filenames added to the 'seen' array are always
added with a path separator at the beginning of the filename, but when
the package dir is walked for comparison, any files at the top-level
will be missing the beginning path separator and the comparison will
fail despite the fact that the file was actually packaged.  This
because the remainder between the dirname and the dvar base name is
used in the path join and in the case of files at the top-level, the
remainder is the empty string, where it should be '/' for comparison
purposes.

(From OE-Core rev: cb19503139b9102f02ba3e5be63d5e85f280f2ef)

Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/package.bbclass

@@ -936,8 +936,11 @@ python populate_packages () {
 
 	unshipped = []
 	for root, dirs, files in os.walk(dvar):
+		dir = root[len(dvar):]
+		if not dir:
+			dir = os.sep
 		for f in files:
-			path = os.path.join(root[len(dvar):], f)
+			path = os.path.join(dir, f)
 			if ('.' + path) not in seen:
 				unshipped.append(path)