graft: introduce --abort flag to abort interrupted graft This patch introduces a new --abort flag to `hg graft` command which aborts an interrupted graft and rollbacks to the state before graft. The behavior when some of grafted changeset get's published while interrupted graft or we have new descendants on grafted changesets is same as that of rebase which is warn the user, don't strip and abort the abort the graft. Tests are added for the new flag. .. feature:: `hg graft` now has a `--abort` flag which aborts the interrupted graft and rollbacks to state before the graft. Differential Revision: https://phab.mercurial-scm.org/D3754

graft: move `if continue` to elif and add new line This will make upcoming patch where we introduce a new elif for the abort case more readable. Also added a new line before the if-else starts. Differential Revision: https://phab.mercurial-scm.org/D3752

graft: start storing new nodes formed in graftstate This patch starts storing the new nodes formed during the ongoing graft operation in the graftstate. We need the list of new nodes formed while implmenting `graft --abort` which will strip out the new nodes. Differential Revision: https://phab.mercurial-scm.org/D3751

show: use filter() function to strip "tip" tag Before, an empty tag "" was inserted in place of "tip", resulting in double spaces.

templater: extend filter() to accept template expression for emptiness test This utilizes the pass-by-name nature of template arguments.

templater: introduce filter() function to remove empty items from list The primary use case is to filter out "tip" from a list of tags.

templater: fix truth testing of integer 0 taken from a list/dict Broken at f9c426385853. bool(python_value) shouldn't be used here since an integer 0 has to be truthy for backward compatibility.

formatter: look for template symbols from the associated name Otherwise symbolsused() would fail if a named template is specified with -T.