contrib: make check-code.py check code fragments embedded in test scripts

contrib: add line offset information to file check function of check-code.py This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. This information will be useful to show correct line number in an actual file for errors detected in code fragments embedded in *.t test scripts.

contrib: change return value of file checking function of check-code.py This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. After this patch, caller of _checkfiledata() can count number of errors in each code fragments of an actual file. This will be useful to share --per-file limitation by all embedded code fragments.

contrib: factor out actual error check for file data of check-code.py This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. Newly added _checkfiledata() will be useful to apply checks on code fragments embedded in *.t test scripts.

contrib: refactor preparation logic for patterns of check-code.py This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. Before this patch, preparation logic in _preparepats() of check-code.py is not reusable. It can handle only module global list "checks". This patch splits preparation logic into small internal functions, and add the loop to invoke them, in order to increase reusability of the logic. "c[-2]" is equivalent to "c[3]" for "checks". This patch uses the former, because it will be more reusable for subsequent patch than the latter.

contrib: split pypats list in check-code.py This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. Ideally, all patterns in "pypats" before this patch should be applied on not only normal *.py files but also code fragments embedded in *.t test scripts. But fixing test scripts for some patterns requires many changes, and has less profit than effort. Therefore, this patch splits pypats list into two below: - commonpypats, which are applied on all (= including code fragments embedded in *.t test scripts) *.py files - pypats, which are applied only on normal *.py

tests: remove useless line wrapping in a code fragment embedded in test script This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. This revision avoids error of check-code.py below. Use () to wrap long lines in Python, not \

storage: introduce a `revlog.reuse-external-delta` config This option goes a bit further and provides a way to get the same behavior as the `re-delta-all` optimisation from `hg debugupgraderepo`. The effect of the option is a bit hard to test as we do not have multiple diff algorithm at hand. However, we at least make sure the code path run.

storage: introduce a `revlog.reuse-external-delta-parent` config As pointed in c59987ab96b4, we had no simple way to get a client to not blindly reuse the delta parent from a bundle. Instead one had to rely on a side effect of the deprecated `format.generaldelta` configuration. We introduce an explicit `revlog.reuse-external-delta-parent` configuration option (default to True) to control this behavior. If the option is not set, `format.generaldelta` still control this behavior. To test the new option, we convert a couple of place where `generaldelta` have been used for its side effects.

merge with stable