If a pack isn't found on disk remove it from pack list

If accessing a pack throws FileNotFoundException the pack was deleted
and we need to remove it from the pack list. This can be caused e.g. by
git gc.

Change-Id: I5d10f87f364dadbbdbfb61b6b2cbdee9c7457f3d
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

 packRefs=Pack refs
 packSizeNotSetYet=Pack size not yet set since it has not yet been received
 packTooLargeForIndexVersion1=Pack too large for index version 1
+packWasDeleted=Pack file {0} was deleted, removing it from pack list
 packWriterStatistics=Total {0,number,#0} (delta {1,number,#0}), reused {2,number,#0} (delta {3,number,#0})
 panicCantRenameIndexFile=Panic: index file {0} must be renamed to replace {1}; until then repository is corrupt
 patchApplyException=Cannot apply: {0}

org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java

 	/***/ public String packRefs;
 	/***/ public String packSizeNotSetYet;
 	/***/ public String packTooLargeForIndexVersion1;
+	/***/ public String packWasDeleted;
 	/***/ public String packWriterStatistics;
 	/***/ public String panicCantRenameIndexFile;
 	/***/ public String patchApplyException;

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java

 			tmpl = JGitText.get().corruptPack;
 			// Assume the pack is corrupted, and remove it from the list.
 			removePack(p);
+		} else if (e instanceof FileNotFoundException) {
+			tmpl = JGitText.get().packWasDeleted;
+			removePack(p);
 		} else {
 			tmpl = JGitText.get().exceptionWhileReadingPack;
 			// Don't remove the pack from the list, as the error may be