[Bug-tar] 1.15.1 -> 1.20 listed-incremental causes reversion to level 0 dump

[Erik Bryer]

Moving from GNU tar version 1.15.1 to 1.20 causes a level 0 dump. I searched 
the manual and the mailing list archives, but I found no mention of this.

The online manual (http://www.gnu.org/software/tar/manual/tar.html#SEC172) 
states "GNU tar version 1.22 supports three snapshot file formats": format 0, 
format 1, and its native format, format 2. However, when I feed a snapshot file 
made with version 1.15.1 GNU tar (capable only of level 0 snapshot files) to 
1.20 GNU tar, it routinely overwrites the snapshot file with the level 2 
version and populates the new tar file with all data, not just what has changed.

Here are the commands I used on some test directories and their result:
# /bin/tar --version
tar (GNU tar) 1.15.1
# /bin/tar --create --file=./foo.1.tar --listed-incremental=./foo.snap 
./Binaries
# /bin/tar --create --file=./foo.2.tar --listed-incremental=./foo.snap 
./Binaries
# /bin/tar --create --file=./foo.3.tar --listed-incremental=./foo.snap 
./Binaries/ ./backup-progs
# strings foo.snap | head
GNU tar-1.22-2
1263621813
180228000
1241196232
2049
9899855
./Binaries/areca/archttpsrv/V1.82_70911/x86-64
Yarchttp64
Yarchttp64.log
Yarchttpsrv.conf
# ls -ltrh foo*
-rw-r--r-- 1 root root  34M Jan 16 00:59 foo.1.tar
-rw-r--r-- 1 root root  40K Jan 16 01:01 foo.2.tar
-rw-r--r-- 1 root root 130K Jan 16 01:02 foo.3.tar
-rw-r--r-- 1 root root 6.5K Jan 16 01:03 foo.snap
-rw-r--r-- 1 root root  55M Jan 16 01:03 foo.4.tar
# du -sh Binaries/ backup-progs/ files-count/
34M     Binaries/
240K    backup-progs/
22M     files-count/

-Erik