Adds 'head' as revision for Subversion repositories

To still support the editor plugin, a new field in the
browse command results is needed to indicate, whether
such a result or rather the requested revision can be
modified by a new commit.

This is the case, when
- for Subversion repositories either the new 'head' or the
latest revision has been requested, or
- for Git and HG when a branch (or the default by specifying
no concrete revision) has been used.

scm-plugins/scm-git-plugin/src/test/java/sonia/scm/repository/spi/GitBrowseCommandTest.java

@@ -54,11 +54,27 @@ public class GitBrowseCommandTest extends AbstractGitCommandTestBase {
     BrowseCommandRequest request = new BrowseCommandRequest();
     request.setPath("a.txt");
     BrowserResult result = createCommand().getBrowserResult(request);
+    assertTrue(result.isModifiable());
+    assertEquals("HEAD", result.getRequestedRevision());
     FileObject fileObject = result.getFile();
     assertEquals("a.txt", fileObject.getName());
     assertFalse(fileObject.isTruncated());
   }
 
+  @Test
+  public void testDifferentBranch() throws IOException {
+    BrowseCommandRequest request = new BrowseCommandRequest();
+    request.setRevision("test-branch");
+
+    BrowserResult result = createCommand().getBrowserResult(request);
+
+    assertTrue(result.isModifiable());
+    Collection<FileObject> foList = result.getFile().getChildren();
+    assertThat(foList)
+      .extracting("name")
+      .containsExactly("c", "a.txt");
+  }
+
   @Test
   public void testDefaultDefaultBranch() throws IOException {
     // without default branch, the repository head should be used