phases: add a mutable boolean property on context

ignore: add files present in the hackable-hg windows distribution

graft: use consistent language in help Removes the word 'aborted' from the 3rd paragraph in favor of 'interrupted', the same word used in the description of the -c/--continue switch. The word 'interrupted' is also consistent with the help for rebase.

merge with stable

largefiles: copy files in binary mode (issue3164)

diff: when diffing a revision with a deleted subrepo, maintain the node context (issue3153)

phases: add a function to compute visible heads This function will be used to hide secret changeset.

phases: Add a third phase for secret changeset