Externalize error message used in CheckoutCommand

Change-Id: Ifbc469b07e63218107157ffbf23ae55c52a55ef4
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

@@ -44,6 +44,7 @@ cannotBeCombined=Cannot be combined.
 cannotBeRecursiveWhenTreesAreIncluded=TreeWalk shouldn't be recursive when tree objects are included.
 cannotChangeActionOnComment=Cannot change action on comment line in git-rebase-todo file, old action: {0}, new action: {1}.
 cannotChangeToComment=Cannot change a non-comment line to a comment line.
+cannotCheckoutOursSwitchBranch=Checking out ours/theirs is only possible when checking out index, not when switching branches.
 cannotCombineSquashWithNoff=Cannot combine --squash with --no-ff.
 cannotCombineTreeFilterWithRevFilter=Cannot combine TreeFilter {0} with RevFilter {1}.
 cannotCommitOnARepoWithState=Cannot commit on a repo with state: {0}

org.eclipse.jgit/src/org/eclipse/jgit/api/CheckoutCommand.java

@@ -673,7 +673,6 @@ public class CheckoutCommand extends GitCommand<Ref> {
 	private void checkOptions() {
 		if (checkoutStage != null && !isCheckoutIndex())
 			throw new IllegalStateException(
-					"Checking out ours/theirs is only possible when checking out index, "
-							+ "not when switching branches.");
+					JGitText.get().cannotCheckoutOursSwitchBranch);
 	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java

@@ -103,6 +103,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String cannotBeRecursiveWhenTreesAreIncluded;
 	/***/ public String cannotChangeActionOnComment;
 	/***/ public String cannotChangeToComment;
+	/***/ public String cannotCheckoutOursSwitchBranch;
 	/***/ public String cannotCombineSquashWithNoff;
 	/***/ public String cannotCombineTreeFilterWithRevFilter;
 	/***/ public String cannotCommitOnARepoWithState;