Add a new superblock field, s_mkfs_time, which indicates when
the filesystem was created.  It is set via mke2fs, and printed 
via list_super2() (which is called by dumpe2fs).  

Also, list_super2() will now print "n/a" if the last mount time
(s_mtime) is zero.

diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
index d9be945..ecb27d7 100644
--- a/lib/ext2fs/initialize.c
+++ b/lib/ext2fs/initialize.c
@@ -127,7 +127,7 @@
 	}
 
 	set_field(s_checkinterval, EXT2_DFL_CHECKINTERVAL);
-	super->s_lastcheck = time(NULL);
+	super->s_mkfs_time = super->s_lastcheck = time(NULL);
 
 	super->s_creator_os = CREATOR_OS;