fix for bug #244217

Initial Mail retrieval from POP account fails(mac only)

the problem is that on the mac, nsPersistentFileDescriptor::operator= will fail silently if the file doesn't exist.
(that issue will be spun off)

on the mailnews side, we can create the msf file

r/sr=bienvenu

mailnews/base/util/nsMsgDBFolder.cpp

@@ -1086,6 +1086,10 @@ nsresult nsMsgDBFolder::GetFolderCacheKey(nsIFileSpec **aFileSpec)
 			nsLocalFolderSummarySpec summarySpec(folderName);
 
 			dbPath->SetFromFileSpec(summarySpec);
+
+			// create the .msf file
+			// see bug #244217 for details
+			dbPath->Touch();
 		}
 	}
 	return rv;