Add DiffConflictsWithHistory to split the diff view and open the history

Closes #15. Credit to @jmandawg and @transamericamoon for the addition.

Author: whiteinge

README.md

@@ -77,6 +77,13 @@ splitting them apart.
     git config --global mergetool.keepBackup false
     ```
 
+    Or, if you'd prefer to always open both the diff view and the history view
+    call `DiffConflictsWithHistory` instead:
+
+    ```
+    git config --global mergetool.diffconflicts.cmd 'vim -c DiffConflictsWithHistory "$MERGED" "$BASE" "$LOCAL" "$REMOTE"'
+    ```
+
 3.  During a merge you can call `:DiffConflictsShowHistory` to open a new tab
     containing the merge BASE and full copies of the LOCAL and REMOTE versions
     of the conflicted file. This can help to understand the history or intent

doc/diffconflicts.txt

@@ -11,9 +11,16 @@ git config --global mergetool.diffconflicts.trustExitCode true
 git config --global mergetool.keepBackup false
 
 Commands:
+:DiffConflicts
+	Convert a file containing Git conflict markers into a two-way diff.
+
 :DiffConflictsShowHistory
         Open a new tab containing the merge base and the local and remote
         version of the conflicted file.
 
+:DiffConflictsWithHistory
+	Call both DiffConflicts and DiffConflictsShowHistory. This is useful in
+	the Git mergetool configuration to always open the history by default.
+
 						*DiffConflicts-settings*
 This plugin doesn't have any settings.

plugin/diffconflicts.vim

@@ -92,26 +92,23 @@ function! s:checkThenShowHistory()
     endif
 endfunction
 
-function! s:checkThenDiff(showHist)
+function! s:checkThenDiff()
     if (s:hasConflicts())
-      call s:diffconfl()
-      if (a:showHist)
-        call s:checkThenShowHistory()
-        tabfirst
-      endif
-      redraw
-      echohl WarningMsg
-         \ | echon "Resolve conflicts leftward then save. Use :cq to abort."
-         \ | echohl None
+        redraw
+        echohl WarningMsg
+            \ | echon "Resolve conflicts leftward then save. Use :cq to abort."
+            \ | echohl None
+        return s:diffconfl()
     else
         echohl WarningMsg | echo "No conflict markers found." | echohl None
     endif
 endfunction
 
-
-command! DiffConflicts call s:checkThenDiff(0)
-command! DiffConflictsWithHistory call s:checkThenDiff(1)
+command! DiffConflicts call s:checkThenDiff()
 command! DiffConflictsShowHistory call s:checkThenShowHistory()
+command! DiffConflictsWithHistory call s:checkThenShowHistory()
+    \ | 1tabn
+    \ | call s:checkThenDiff()
 
 let &cpo = s:save_cpo
 unlet s:save_cpo