chg: fallback to original hg for some unsupported commands or flags There are some known unsupported commands or flags for chg, such as hg serve -d and hg foo --time. This patch detects these situations and transparently fall back to the original hg. So the users won't bother remembering what chg can and cannot do by themselves. The current detection is not 100% accurate since we do not have an equivalent command line parser in C. But it tries not to cause false positives that prevents people from using chg for legit cases. In the future we may want to implement a more accurate "unsupported" check server-side.