[OE-core] About PV = "0.0+git${SRCPV}"

[Robert Yang]

There are several recipes in oe-core which has:
PV = "0.0+git${SRCPV}"

These recipes don't have a release version, so we use "0.0+git${SRCPV}",
but the package manager such as opkg/rpm/smart may not upgrade them
correctly when the recipes is upgraded since we can't make sure that
SRCPV_new > SRCPV_old.

How about we use date for these recipes which doesn't have a release
version? For example, if we integrate them to oe-core today, then
PV = "20160421". And when we upgrade them in the future, we can change
the PV to that day. We can change all the current version 0.0 target
recipes to today, and add a sanity check for version 0.0.

-- 
Thanks

Robert