[Bug-apl] popen() and pclose() in FILE_IO

[Juergen Sauermann]

Hi,

I have added functions popen() and pclose() to the native FILE_IO 
function, see SVN 212.

That makes it possible, for example,  to call programs from GNU APL and 
return their output
directly to GNU APL rather than needing to store the output of the 
command in an intermediate
file and reading it back.

An example of how to use this is given near the end of testcases/File_IO.tc.

/// Jürgen