patch for memory overrun on Linux(i386)

Hi,

It turns of that one of the bugs I detected with Electric Fence
is caused by an assumption that memory return by palloc and malloc 
is aligned on 8 bytes boundaries (double alignment). 
Adjusting this to correspond with the reality of the malloc
implementation on my pentium based linux box fixes the problem.

The following simple patch to include/utils/memutils.h
will fix the problem.

85c85
< #if ! defined(sco)
---
> #if ! defined(sco) && !defined(linux)

There is still another buffer overrun which I will try to find. 
The remaining one is triggered by creating a sequence.

I hope this patch will be applied if it makes sense to 
you guys.

With regards from Maurice.