Merge branch 'rs/xdiff-merge-overlapping-hunks-for-W-context' into maint

"git diff -W" output needs to extend the context backward to include the header line of the current function and also forward to include the body of the entire current function up to the header line of the next one. This process may have to merge to adjacent hunks, but the code forgot to do so in some cases. * rs/xdiff-merge-overlapping-hunks-for-W-context: xdiff: fix merging of hunks with -W context and -u context