fromfile parser does not support escaping prefix character

[alokpr]

I did not find any documentation on how to escape the prefix character if needed. And none of my attempts were successful:

• myprog @@escaped-arg
• myprog '@escaped-arg'

In both of these cases, argfile attempts to read the non-existent "[@]escaped-arg" file.

[epage]

iirc when I looked into this, I did not see an implementation that supported escaping, e.g. python's