[slim-vim] ECL Vim FFI, buffer writing bugs

[Brad Beveridge]

There are subtle bugs somewhere in the ECL/Vim interface.
I can see them when I
1) Split the screen into 2 buffers, set one to be a lisp file and one
to be the --debug-sv-- buffer
2) The lisp file has some functions that are medium size, and I call
(disassemble 'func) on them, producing 80 odd notes and quite a bit of
output.

The Vim buffers go strange, text gets a bit messed up, ie - some text
(with its colouring) from the Lisp buffer gets pushed into the
--debug-sv-- buffer.
Some of the text in each buffer can get "moved around" it looks sort
of right, but off by a line or an indent.
ECL/Vim can and will crash with a Segmentation violation.  It crashes
to the ECL console most often, so I think something in there is the
problem.  It looks a little like the GC bug we used to have, maybe
adding GC for the whole Vim image could be a good idea.
Also, I am writing the text out to a buffer from within an ECL
callback, so that could be an area of issue.

So I am going to try and produce some test suites to attempt to repro
these bugs, but any help would be very much appreciated.

Cheers
Brad