This was used to cache a narrow string representation
of commands, so that if certain system calls returned errors
after fork, we could output error messages without allocating
memory. But in practice these errors are very uncommon, as are
commands that have wide characters. It is simpler to do a best-effort
output of the wide string, instead of caching a narrow string
unconditionally.
If stdio is dead due to EPIPE, there's no great reason to spew a stack dump.
This will still write an error to stderr if stdout dies. This might be
undesirable, but changing that should be considered separately.
This change moves source files into a src/ directory,
and puts object files into an obj/ directory. The Makefile
and xcode project are updated accordingly.
Fixes#1866
