[OE-core] FETCHCMD drop breaks build when append is used (from patch b259bd31eb)

[Andrey Zhizhikin]

Hello Andre,

I've just pulled the master and experienced a build failure during
fetching of updated recipe's source tarballs.

The reason for this being that defaults for FETCHCMD has been dropped
with your patch b259bd31eb from the series. Once defaults are removed
and appends are used - the FETCHCMD gets defined to the value listed
in append, which normally does not contain a command itself rather
than necessary additional parameters (like user/passwd if working with
local pre-mirror servers).

This patch would also break several other recipes which are using
appends to FETCHCMD, for example for FETCHCMD_wget the libedit would
fail since it appends the wget to use different User-Agent.

I've copied Raj here since he introduced this recipe in the form it is
and would definitely break.

Can you please have a look at this and advise on how one can continue
to use the FETCHCMD appends for the future?

For now, I've defined the FETCHCMD_wget in my local.conf but I do not
believe that this is the general way everyone should follow if they
would need to append fetcher commands...

Thanks a lot!

-- 
Regards,
Andrey.