Fix issues with merge algorithm

[le-git-imate]

Description of issue or feature request
The merge algorithm can not support some merge requests due to issues in two functions:(1) xmerge/xdl_refine_conflicts, (2) xdiffi/xdl_split.

You can replicate the issue in the xdl_refine_conflicts function, if, for example, you perform the following PRs by the le-git-imate extension:
golang/go#33882
github/gitignore#3121

You can replicate the issue in xdl_split function, if, for example, you perform the following PRs by the le-git-imate extension:
vuejs/vue#10167
golang/go#33870
facebook/react#16591
ytdl-org/youtube-dl#22063

Current behavior

• le-git-imate does not perform merge requests if xmerge/xdl_refine_conflicts and xdiffi/xdl_split functions get involved.

Expected behavior

• Fix issues with xdl_refine_conflicts and xdl_split functions. This can be done as part of Improve the merge algorithm #32.