Debian での「+b#」パッケージのバージョンはどういう意味ですか？

今日のアップグレードを確認しましたが、Debianテストで63のアップグレードを見ました。美しい。ほとんどが維持されているので、-Vこれらのバージョンを頻繁に見ることができるので疑問に思います。驚いたことに、ほとんどがまたは+b1バージョン+b2にアップグレードされました。私は良い男の子のようにバージョンなしでapt-get changelog libc6変更ログを見るためにこれを行いました（はい、重要です）。+b1それでは、このバージョンはどんな用途に適していますか？

sudo apt-get -V upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages have been kept back:
   gdm3 (3.4.1-9 => 3.4.1-9+b1)
   libalgorithm-diff-xs-perl (0.04-2+b2 => 0.04-2+b3)
   libapt-pkg-perl (0.1.29 => 0.1.29+b1)
   libcairo-perl (1.103-2 => 1.103-2+b1)
   libclass-c3-xs-perl (0.13-1+b2 => 0.13-1+b3)
   libclone-perl (0.34-1 => 0.34-1+b1)
   libcrypt-blowfish-perl (2.14-1 => 2.14-1+b1)
   libcrypt-openssl-bignum-perl (0.04-4 => 0.04-4+b1)
   libcrypt-ssleay-perl (0.58-1 => 0.58-1+b1)
   libdbd-mysql-perl (4.023-1 => 4.023-1+b1)
   libdbi-perl (1.628-1 => 1.628-1+b1)
   libdigest-crc-perl (0.18-1+b1 => 0.18-1+b2)
   libdigest-md4-perl (1.9+dfsg-1 => 1.9+dfsg-1+b1)
   libfile-fcntllock-perl (0.14-2 => 0.14-2+b1)
   libfile-fnmatch-perl (0.02-1+b2 => 0.02-1+b3)
   libglib-perl (1.301-1 => 1.301-1+b1)
   libgtk2-perl (1.247-2 => 1.247-2+b1)
   libhtml-parser-perl (3.71-1 => 3.71-1+b1)
   libio-pty-perl (1.08-1+b2 => 1.08-1+b3)
   libjson-xs-perl (2.340-1 => 2.340-1+b1)
   liblist-moreutils-perl (0.33-1+b1 => 0.33-1+b2)
   liblocale-gettext-perl (1.05-7+b1 => 1.05-7+b2)
   libmath-bigint-gmp-perl (1.37-2 => 1.37-3)
   libnet-dbus-perl (1.0.0-2 => 1.0.0-2+b1)
   libnet-dns-perl (0.68-1.1 => 0.68-1.2)
   libnet-pcap-perl (0.17-1 => 0.17-1+b1)
   libnet-rawip-perl (0.25-1+b2 => 0.25-1+b3)
   libnet-ssleay-perl (1.55-1 => 1.55-1+b2)
   libpam-systemd (44-12 => 44-12+b1)
   libpango-perl (1.224-2 => 1.224-2+b1)
   libparams-util-perl (1.07-1 => 1.07-1+b1)
   libpurple0 (2.10.7-2 => 2.10.7-2+b1)
   libsocket-perl (2.011-1 => 2.011-1+b1)
   libsocket6-perl (0.23-1+b2 => 0.23-1+b3)
   libsub-name-perl (0.05-1+b2 => 0.05-1+b3)
   libsvn1 (1.6.17dfsg-4.1+b1 => 1.7.9-1+nmu4)
   libterm-readkey-perl (2.30-4+b2 => 2.30-4+b3)
   libterm-readline-gnu-perl (1.20-2+b1 => 1.20-2+b2)
   libtext-charwidth-perl (0.04-7+b1 => 0.04-7+b2)
   libtext-iconv-perl (1.7-5 => 1.7-5+b1)
   libuuid-perl (0.02-5 => 0.02-5+b1)
   libxml-libxml-perl (2.0010+dfsg-1 => 2.0010+dfsg-1+b1)
   libxml-parser-perl (2.41-1+b1 => 2.41-1+b2)
   libyaml-libyaml-perl (0.38-3 => 0.38-3+b1)
   perl (5.14.2-21 => 5.18.1-3)
   perl-base (5.14.2-21 => 5.18.1-3)
   perl-modules (5.14.2-21 => 5.18.1-3)
   perl-tk (804.031-1 => 804.031-1+b1)
   subversion (1.6.17dfsg-4.1+b1 => 1.7.9-1+nmu4)
   systemd (44-12 => 44-12+b1)
   vim (7.3.923-3 => 7.3.923-3+b1)
   vim-common (7.3.923-3 => 7.3.923-3+b1)
   vim-gtk (7.3.923-3 => 7.3.923-3+b1)
   xchat (2.8.8-7.1 => 2.8.8-7.1+b1)
   xserver-xorg-core (1.12.4-6.1 => 1.12.4-6.2+b1)
The following packages will be upgraded:
   libc-dev-bin (2.17-92 => 2.17-92+b1)
   libc6 (2.17-92 => 2.17-92+b1)
   libc6-dbg (2.17-92 => 2.17-92+b1)
   libc6-dev (2.17-92 => 2.17-92+b1)
   libc6-i686 (2.17-92 => 2.17-92+b1)

apt-cache policy libc6
libc6:
  Installed: 2.17-92
  Candidate: 2.17-92+b1
  Version table:
     2.17-92+b1 0
        500 http://ftp.us.debian.org/debian/ testing/main i386 Packages
        500 http://http.debian.net/debian/ jessie/main i386 Packages
 *** 2.17-92 0
        100 /var/lib/dpkg/status

apt-get changelog libc6
eglibc (2.17-92) unstable; urgency=low

  * kfreebsd/local-sysdeps.diff: update to revision 4839 (from glibc-bsd).

 -- Petr Salinger <[email protected]>  Wed, 31 Jul 2013 22:38:47 +0100

eglibc (2.17-91) unstable; urgency=low

  [ Petr Salinger ]
  * switch libpthread implementation on kfreebsd-* to fbtl.
    Closes: #703545. Closes: #665287. Closes: #683825. Closes: #489066.
  * split some parts of kfreebsd/local-linuxthreads29.diff
    into  kfreebsd/local-nscd-no-sockcloexec.diff and
          kfreebsd/local-linuxthreads-tlsdesc.diff
  * add kfreebsd/local-fbtl.diff and kfreebsd/local-fbtl-depends.diff
  * kfreebsd/local-sysdeps.diff: update to revision 4809 (from glibc-bsd).
    Closes: #718181. Addresses: #717032 in new binutils.
  * update testsuite-checking/expected-results-*-kfreebsd-gnu-*
    by fbtl tests that are known to fail.
(snip)