allow to pass filename in autocmd parameter

[landru29]

if autocmd parameter is -autocmd='@/path/to/text/file, the content of the file is injected

[ColinPitrat]

I'm not entirely sold to the idea. Passing a file is very useful but this can already be done with something like:

./cap32 -a `cat /tmp/myprog.bas`

Which I use regularly in conjunction with removing the speed limit to type long listings quickly.