resolve: perform all premerges before performing any file merges (BC) Just like the BC to merge before it, this allows for a maximally consistent state before providing any prompts to the user.

test-resolve.t: add some tests for .orig file contents An upcoming patch will touch some code around this area, and I couldn't find any tests related to this.

test-resolve.t: add some output to show order of operations This basically shows the behavior of resolve with multiple files. An upcoming behavior change will cause this output to also change.

merge.mergestate: perform all premerges before any merges (BC) We perform all that we can non-interactively before prompting the user for input via their merge tool. This allows for a maximally consistent state when the user is first prompted. The test output changes indicate the actual behavior change happening.

merge: introduce a preresolve function The section of code that writes out the version of the file cached in the merge state should only be run at preresolve time. This is so that if the premerge keeps around conflict markers, those don't get overwritten before the main merge.

merge.mergestate._resolve: also return completed status We'll need this for a new 'preresolve' function we're adding.