The equivalent interpreter option is set by wrapper.exe, but this *.bat file is
what gets installed in a venv. Without this mode, any command that spins up a
pager has no output, unless the pager is explicitly disabled. The variable is
set inside the setlocal scope to keep it from leaking into the environment
after the bat file exits.
We should probably still figure out how to ship a compiled hg.exe when
installing with pip, because the binary does other things like enable long
filename support. But this avoids the dangerous and confusing lack of output in
the meantime.