commit: block amend while histedit is in progress (issue4800)

chg: limit reconnect attempts Some users may have hg as a wrapper script which sets sensitive environment variables (like setting up virtualenv). This will make chg redirect forever because the environment variables are never considered up to date. This patch adds a limit (10) for reconnect attempts and warn the user with a possible solution if the limit is exceeded.

chg: use validate to make sure the server is up to date This patch uses the newly added validate method to make sure the server has loaded the up-to-date config and extensions. If the server cannot validate itself, the client will receive instructions and follow them to try to reach another server that is more likely to validate itself. The instructions can be a redirect (connect to another server address) and/or an unlink (stops an out-dated server).

chg: implement validate in hgclient This patch implements the corresponding validate method in hgclient. It will return instruction strings as is without taking any real action.

hgclient: use absolute_import and print_function

fixpax: use absolute_import and print_function

debugcmdserver: use absolute_import and print_function

check-config: use absolute_import and print_function

casesmash: use absolute_import

chgserver: implement validate command validate will load the repo config and check if the server has up-to-date config to continue serve the client. In case it does not, the server will send instructions to the client about what to do next, including to retry with a different address or to unlink an outdated socket file to stop an old server.