Allow setting the environment. Due to a subprocess quirk, it must
always be set explicitly (reuses the one from the previous call if not
set, instead of falling back to os.environ).
Embedding nul characters will be useful for parsing git output more
reliably; support dumping such output a bit better.
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
