merge: pass wctx to premerge, filemerge
In the in-memory merge branch. we'll need to call a function (``flushall``) on
the wctx inside of _xmerge.
This prepares the way so it can be done without hacks like ``fcd.ctx()``.
Differential Revision: https://phab.mercurial-scm.org/D449
$ hg init t
$ cd t
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ rm b
$ hg update 0
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo This is file b2 > b
$ hg add b
$ hg commit -m "commit #2"
created new head
$ cd ..; rm -r t
$ mkdir t
$ cd t
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ rm b
$ hg update 0
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo This is file b2 > b
$ hg commit -A -m "commit #2"
adding b
created new head
$ cd ..; rm -r t
$ hg init t
$ cd t
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ rm b
$ hg remove b
$ hg update 0
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ echo This is file b2 > b
$ hg commit -A -m "commit #2"
adding b
created new head
$ cd ..