Add link for image file

* Render image tag with link tag on issue and wiki
* Correct response content-type of attached image on issue

src/main/scala/app/IssuesController.scala

@@ -275,7 +275,10 @@ trait IssuesControllerBase extends ControllerBase {
 
   get("/:owner/:repository/_attached/:file")(referrersOnly { repository =>
     defining(new java.io.File(Directory.getAttachedDir(repository.owner, repository.name), params("file"))){ file =>
-      if(file.exists) file else NotFound
+      if(file.exists) {
+        contentType = FileUtil.getMimeType(file)
+        file
+      } else NotFound
     }
   })
 

src/main/scala/util/FileUtil.scala

@@ -5,9 +5,13 @@ import java.net.URLConnection
 import java.io.File
 import util.ControlUtil._
 import scala.util.Random
+import eu.medsea.mimeutil.{MimeUtil2, MimeType}
 
 object FileUtil {
 
+  private val mimeUtil = new MimeUtil2()
+  mimeUtil.registerMimeDetector("eu.medsea.mimeutil.detector.MagicMimeMimeDetector")
+
   def getMimeType(name: String): String =
     defining(URLConnection.getFileNameMap()){ fileNameMap =>
       fileNameMap.getContentTypeFor(name) match {
@@ -16,6 +20,16 @@ object FileUtil {
       }
     }
 
+  /**
+   * Returns mime type detected by file content.
+   *
+   * @param file File object
+   * @return mime type String
+   */
+  def getMimeType(file: File): String = {
+    MimeUtil2.getMostSpecificMimeType(mimeUtil.getMimeTypes(file, new MimeType("application/octet-stream"))).toString
+  }
+
   def getContentType(name: String, bytes: Array[Byte]): String = {
     defining(getMimeType(name)){ mimeType =>
       if(mimeType == "application/octet-stream" && isText(bytes)){

src/main/scala/view/Markdown.scala

@@ -89,7 +89,8 @@ class GitBucketHtmlSerializer(
   ) with LinkConverter with RequestCache {
 
   override protected def printImageTag(imageNode: SuperNode, url: String): Unit =
-    printer.print("<img src=\"").print(fixUrl(url)).print("\"  alt=\"").printEncoded(printChildrenToString(imageNode)).print("\"/>")
+    printer.print("<a target=\"_blank\" href=\"").print(fixUrl(url)).print("\">")
+           .print("<img src=\"").print(fixUrl(url)).print("\"  alt=\"").printEncoded(printChildrenToString(imageNode)).print("\"/></a>")
 
   override protected def printLink(rendering: LinkRenderer.Rendering): Unit = {
     printer.print('<').print('a')