problems. Instead, use exec*() functions.
Replace PUSHOUT() macro and string buffers with a function that
operates on data structures.
If it is necessary to copy files into place from staging area, then use
pax to copy them.
Add functions in pexec.c to create a pipe for sending data to a child
process. Replace pipe code in create/perform.c with these functions.
Use these functions instead of command-line arguments when copying files
into place from staging area.
Three system() references remain: @exec, @unexec, and vsystem().
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