py3: replace sys.platform with pycompat.sysplatform (part 1 of 2)...
py3: replace sys.platform with pycompat.sysplatform (part 1 of 2)
sys.platform returns unicode on python 3 world. Our code base has most of the
things bytes because of the transformer. So we have a bytes version of this as
pycompat.sysplatform. This series of 2 patches replaces occurences of
sys.platform with pycompat.sysplatform.