mergestate: introduce a new ACTION_KEEP_NEW
`ACTION_KEEP` is overloaded and it's hard to figure out how we end up with this
KEEP, what was the state of things.
In a previous patch, we introduced `ACTION_KEEP_ABSENT` which represents files
which are kept absent in the working directory.
There is another special case where we keep the file when it's not present on
both ancestor and remote side. We introduce a dedicated action for that.
The goal is to use these information to make bid merge smarter.
Differential Revision: https://phab.mercurial-scm.org/D9002
$ hg init
$ "$PYTHON" -c 'open("a", "wb").write(b"confuse str.splitlines\nembedded\rnewline\n")'
$ hg ci -Ama -d '1 0'
adding a
$ echo clean diff >> a
$ hg ci -mb -d '2 0'
$ hg diff -r0 -r1
diff -r 107ba6f817b5 -r 310ce7989cdc a
--- a/a Thu Jan 01 00:00:01 1970 +0000
+++ b/a Thu Jan 01 00:00:02 1970 +0000
@@ -1,2 +1,3 @@
confuse str.splitlines
embedded\r (no-eol) (esc)
newline
+clean diff