Re: [Libvir] Fix buffer overflow in dumping XML

The new bufferContentAndFree() method used for the QEMU daemon rellocs the buffer size down to release memory held by the buffer which was never used for any data. Unfortunately it reallocs it 1 byte too small, so later uses of strlen()/strcpy() either magically work, or randomly append gargage or crash the daemon depending on the phase of the moon :-) Re-allocing the buffer to relase a few bytes memory isn't really an optimization since the caller is going to free the entire block a very short while later, so this patch simply removes the realloc call.

As an aside, the virBuffer functions in src/xml.c and the buffer functions in qemud/buf.c are both flawed wrt to the way they call the Grow method. The method expects the len parameter to be extra bytes needed, but several of the callers pass in the total desired length, so it allocates too much memory. There are various other non-fatal flaws which need to be cleaned up in this code, but the attached patch just focuses on the current fatal buffer overflow for now.