amend: fix unlocking order - first lock then wlock

codingstyle: remove trailing spaces in various text files Better do it once than see random changes in diffs later.

tests: run check-code on Python files without .py extension

histedit: move outgoing processing to its own function Every piece of code extracted from the main command is a win. We simplify changeset determination in the process. Parent ceases being a list before becoming a node. We how have a root variable containing a node all the time.

histedit: move all arguments checks to the beginning of the command This changeset move all checks and raises related to arguments validation to the top of the file. This gathers all the logic in one place and clarifies the code doing actual work. This paves the way for splitting this gigantic function in separated functions. A `goal` variable is introduced in the process. It holds the action to be done by this invocation (new, continue or abort). An invalid invocation is found in the process (the new code is a bit stricter).

histedit-test: generalise --commands "-" usage This is simpler than temporary file version. There some minor test changes since commit messages are no longer modifed. There is still some tests using --commands with a real file.

histedit: allow "-" as a command file When "-" is specified as a command file, we read rules from stdin. Alter a single test to demo the behavior, but most of them could benefit from this. There is minor change in test output resulting from the fact we no longer change log messages.

histedit: properly handle --continue on empty fold When all changes from the fold have been dropped, the --continue code was confused. This changeset handles this case. The test for this case existed but was broken.

histedit-test: replace obscure python script by a plain file One of the tests uses a python script to edit the histedit commands on the fly. It was hard to read and likely to break. This is replaced by a plain command file. Doing so made me discover that the python script is incorrect. The "+6" regexp never matched because the revision number is wrong. This error is kept in the replacement for now. Fixing the histedit command triggers a traceback in histedit. A later changeset will fix the error and restore the intended test.

test: improve documentation of some histedit tests Each test section is clearly separated from the others and gains some helpful documentation.