setup: fix mac build broken by
e42d18538e1d
Sometimes xcodebuild prints warnings to stderr, but runcmd() assumes anything
printed to stderr implies failure. Since runcmd() was originally only
intended to run hg, this was fine until it was pressed into service for
running xcodebuild. Thus: split runcmd() into two parts: runcmd(), which does
the minimal amount of work to run a subprocess, and runhg(), which calls
runcmd().
color: don't mention internal function in docstring
The render_text function actually never existed, the docstring
probably meant the render_effects function instead.