new multipart_buffer patch for libapreq

[jo...@sunstarsys.com]

The patch I posted yesterday has a problem 
dealing with client disconnects - your server will hang if 
the upload is interrupted )!

This new patch should be ok. 
I put a lot of comments in it explaining
what I think is happening with the memory allocation.
I think that under normal conditions this patch should
cope with most of these problems.