JENKINS-16426: back up only directorys in the job directory

pom.xml

@@ -111,6 +111,28 @@
       <version>1.3</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.jenkins-ci.main</groupId>
+      <artifactId>jenkins-core</artifactId>
+      <version>1.409</version>
+      <exclusions>
+        <exclusion>
+          <artifactId>junit</artifactId>
+          <groupId>junit</groupId>
+        </exclusion>
+      </exclusions>
+    </dependency>
+    <dependency>
+      <groupId>org.jenkins-ci.main</groupId>
+      <artifactId>jenkins-test-harness</artifactId>
+      <version>1.409</version>
+      <exclusions>
+        <exclusion>
+          <artifactId>junit</artifactId>
+          <groupId>junit</groupId>
+        </exclusion>
+      </exclusions>
+    </dependency>
   </dependencies>
   <distributionManagement>
     <repository>
@@ -125,8 +147,9 @@
     <pluginManagement>
       <plugins>
         <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-compiler-plugin</artifactId>
-          <version>2.3.2</version>
+          <version>3.0.0</version>
           <executions>
             <execution>
               <id>default-testCompile</id>

src/main/java/org/jvnet/hudson/plugins/thinbackup/backup/HudsonBackup.java

@@ -177,7 +177,7 @@ private void backupJobsDirectory(final File jobsDirectory, final File jobsBackup
 
     for (final String jobName : jobNames) {
       final File jobDirectory = new File(jobsDirectory, jobName);
-      if (jobDirectory.exists()) { // sub jobs e.g. maven modules need not be copied
+      if (jobDirectory.exists() && jobDirectory.isDirectory()) { // sub jobs e.g. maven modules need not be copied
         if (jobDirectory.canRead()) {
           File childJobsFolder = new File(jobDirectory, HudsonBackup.JOBS_DIR_NAME);
           if (childJobsFolder.exists()) { // found CloudBeesFolder