Add git config for conflict style merge/diff3

Add a constant in ConfigConstants, and a ConflictStyle enum in
MergeCommand.

Change-Id: Idf8e036b6b6953bec06d6923a39e5ff30c2da562
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java b/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java
index c611f91..ef56d80 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/api/MergeCommand.java
@@ -87,6 +87,20 @@
 	private ProgressMonitor monitor = NullProgressMonitor.INSTANCE;
 
 	/**
+	 * Values for the "merge.conflictStyle" git config.
+	 *
+	 * @since 5.12
+	 */
+	public enum ConflictStyle {
+
+		/** "merge" style: only ours/theirs. This is the default. */
+		MERGE,
+
+		/** "diff3" style: ours/base/theirs. */
+		DIFF3
+	}
+
+	/**
 	 * The modes available for fast forward merges corresponding to the
 	 * <code>--ff</code>, <code>--no-ff</code> and <code>--ff-only</code>
 	 * options under <code>branch.&lt;name&gt;.mergeoptions</code>.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
index 03c1ef9..3e3d9b5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/ConfigConstants.java
@@ -398,7 +398,15 @@
 	public static final String CONFIG_KEY_FF = "ff";
 
 	/**
+	 * The "conflictStyle" key.
+	 *
+	 * @since 5.12
+	 */
+	public static final String CONFIG_KEY_CONFLICTSTYLE = "conflictStyle";
+
+	/**
 	 * The "checkstat" key
+	 *
 	 * @since 3.0
 	 */
 	public static final String CONFIG_KEY_CHECKSTAT = "checkstat";