DfsPackDescription: New method getTotalFileSize()

In code setting up the compact, we need to iterate over the extensions
and adding their sizes. DfsPackDescription itself is a better place
for this functionality.

Add a getTotalFileSize() method returning the accumulated size of all
extensions in the pack.

Change-Id: Ief378305122ef2e74367ff44d187ee256a6a6964

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java
index d4fe566..7a3c139 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsPackDescription.java
@@ -367,6 +367,19 @@ public long getFileSize(PackExt ext) {
 	}
 
 	/**
+	 * Get total size of the pack, including indexes
+	 *
+	 * @return the size of the pack and all its extensions
+	 */
+	public long getTotalFileSize() {
+		long result = 0;
+		for (long sz : sizeMap) {
+			result += sz;
+		}
+		return result;
+	}
+
+	/**
 	 * Get blockSize of the file, in bytes.
 	 *
 	 * @param ext