[OE-core] Attention all: patches for upstream source will be applied with stricter criteria for context

[Alexander Kanavin]

Hello all,

while updating gnutls to a newer version I came across a rather serious 
issue: the way we patch source code is very lenient about the context 
for the lines to be changed. Basically, it's enough for one line before 
and after the changed line to match, because patch command's default 
setting for 'fuzz factor' allows it. If these lines happen to be 
whitespace or braces, then there's nothing to prevent the patch from 
being applied incorrectly.

Here's a particularly nasty example of this happening completely 
silently (compile step works fine too), with security implications:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=10450

I think this absolutely needs to be fixed. The downside is that this 
will break a lot of patches across all layers - after setting the fuzz 
to zero in oe-core we have 87 recipes that fail to be patched. Maxin and 
I are currently going through them one by one and getting them fixed.

Regards,
Alex