Cosmetic adjustment of relative date format, do not display "0 months"

Though it may seem less precise, "0 months" looks bad and the reference
Git implementation also does not display "0 months"

Change-Id: I488e9c97656f9941788ae88d7c5c1562ab6c26f0

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/RelativeDateFormatterTest.java

@@ -119,10 +119,10 @@ public class RelativeDateFormatterTest {
 
 	@Test
 	public void testFormatYearsMonths() {
-		assertFormat(366, DAY_IN_MILLIS, "1 year, 0 month ago");
+		assertFormat(366, DAY_IN_MILLIS, "1 year ago");
 		assertFormat(380, DAY_IN_MILLIS, "1 year, 1 month ago");
 		assertFormat(410, DAY_IN_MILLIS, "1 year, 2 months ago");
-		assertFormat(2, YEAR_IN_MILLIS, "2 years, 0 month ago");
+		assertFormat(2, YEAR_IN_MILLIS, "2 years ago");
 		assertFormat(1824, DAY_IN_MILLIS, "4 years, 12 months ago");
 	}
 

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

@@ -493,5 +493,6 @@ year=year
 years=years
 yearsAgo={0} years ago
 yearsMonthsAgo={0} {1}, {2} {3} ago
+years0MonthsAgo={0} {1} ago
 treeWalkMustHaveExactlyTwoTrees=TreeWalk should have exactly two trees.
 cannotBeRecursiveWhenTreesAreIncluded=TreeWalk shouldn't be recursive when tree objects are included.

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

@@ -552,6 +552,7 @@ public class JGitText extends TranslationBundle {
 	/***/ public String year;
 	/***/ public String years;
 	/***/ public String yearsAgo;
+	/***/ public String years0MonthsAgo;
 	/***/ public String yearsMonthsAgo;
 	/***/ public String treeWalkMustHaveExactlyTwoTrees;
 	/***/ public String cannotBeRecursiveWhenTreesAreIncluded;

org.eclipse.jgit/src/org/eclipse/jgit/util/RelativeDateFormatter.java

@@ -119,8 +119,10 @@ public class RelativeDateFormatter {
 					JGitText.get().year;
 			long months = round(ageMillis % YEAR_IN_MILLIS, MONTH_IN_MILLIS);
 			String monthLabel = (months > 1) ? JGitText.get().months : //
-					JGitText.get().month;
+					(months == 1 ? JGitText.get().month : "");
-			return MessageFormat.format(JGitText.get().yearsMonthsAgo,
+			return MessageFormat.format(
+					months == 0 ? JGitText.get().years0MonthsAgo : JGitText
+							.get().yearsMonthsAgo,
 					new Object[] { years, yearLabel, months, monthLabel });
 		}