meta/lib/oe/utils.py: Corrected the return value of both_contain()

oe.utils.both_contain() should return the result as "checkvalue" or "", but the latest implement returns as "set(['checkvalue'])" or "";

It causes that bitbake.conf generates the wrong result of COMBINED_FEATURES, which contains the common components in both DISTRO_FEATURE and MACHINE_FEATURES.

For example, build in Dizzy branch, COMBINED_FEATURES is "alsa usbhost ...", but recently, COMBINED_FEATURES is like "set(['alsa']) set(['usbhost']) ...".

---
 meta/lib/oe/utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index bedade2..b8224de 100644
@@ -51,7 +51,7 @@ def both_contain(variable1, variable2, checkvalue, d):
     else:
         checkvalue = set(checkvalue)
     if checkvalue.issubset(val1) and checkvalue.issubset(val2):
-        return checkvalue
+        return " ".join(checkvalue)
     else:
         return ""
 

1.9.1