extensions: peek command table of disabled extensions without importing With chg where demandimport disabled, and if disk cache not warm, it took more than 5 seconds to get "unknown command" error when you typo a command name. This is horrible UX. The new implementation is less accurate than the original one as Python can do anything at import time and cmdtable may be imported from another module, but I think it's good enough. Note that the new implementation has to parse .py files, which is slightly slower than executing .pyc if demandimport is enabled.