Issue #1011: do not serialize JGit commit objects

JGit commit objects are a recursive data structure; they have links to
their parent commits. Serializing a JGit commit will try to recursively
serialize all reachable ancestors as faras they have been loaded. If
that ancestor chain is too long, a StackOverflowError is thrown during
Wicket's page serialization if a page has a reference to sucha JGit
commit.

Fixed by making sure that pages o not contain references to JGit
commits. Use the (existing) wrapper object RepositoryCommit instead.

* RepositoryCommit has a transient reference to the JGit commit and
  reads the commit from the repository upon de-serialization.
* RefModel is a similar case (JGit tags/branches may also have links
  to the commits they point to). Solved a bit differently by making it
  a pure data object by transferring the interesting data from the JGit
  object in the constructor.
* Change DataViews instantiated with RevCommit to use RepositoryCommit
  instead.
* Change inner anonymous DataViews to ensure they do not have a
  synthesized field referencing the "allRefs" map. Such a synthesized
  field would also get serialized, and then serialize JGit commits
  again.
  
Finally, remove non-transient logger instances in Wicket classes. Those
might lead to NotSerializableException.

These StackOverflowErrors have been reported in several places since
2014:

* https://groups.google.com/forum/#!topic/gitblit/GH1d8WSlR6Q
* https://bugs.chromium.org/p/gerrit/issues/detail?id=3316
* https://groups.google.com/d/msg/repo-discuss/Kcl0JIGNiGk/0DjH4mO8hA8J
* https://groups.google.com/d/msg/repo-discuss/0_P6A3fjTec/2kcpVPIUAQAJ
* https://github.com/gitblit/gitblit/issues/1011
* https://github.com/tomaswolf/gerrit-gitblit-plugin/issues/21

1 files changed, 1 insertions, 1 deletions

diff --git a/src/main/java/com/gitblit/wicket/pages/EditFilePage.java b/src/main/java/com/gitblit/wicket/pages/EditFilePage.java
index dbf8a79e..5ec9b6ee 100644
--- a/src/main/java/com/gitblit/wicket/pages/EditFilePage.java
+++ b/src/main/java/com/gitblit/wicket/pages/EditFilePage.java
@@ -123,7 +123,7 @@ public class EditFilePage extends RepositoryPage {
 					try {			
 						ObjectId docAtLoad = getRepository().resolve(commitIdAtLoad.getObject());
 						
-						logger.trace("Commiting Edit File page: " + commitIdAtLoad.getObject());
+						logger().trace("Commiting Edit File page: " + commitIdAtLoad.getObject());
 						
 						DirCache index = DirCache.newInCore();
 						DirCacheBuilder builder = index.builder();