fixup the "maintenance track" lines back to 5.6

starting with 5.18 the "maintenance track" started with RCs or .0,
so go back in time and fix it up for the old versions

Author: book

pod/perlhist.pod

@@ -361,9 +361,8 @@ the strings?).
           5.6.0-RC2     2000-Mar-14     Release candidate 2.
           5.6.0-RC3     2000-Mar-21     Release candidate 3.
 
- Sarathy  5.6.0         2000-Mar-22
-
- Sarathy  5.6.1-TRIAL1  2000-Dec-18     The 5.6 maintenance track.
+ Sarathy  5.6.0         2000-Mar-22     The 5.6 maintenance track.
+          5.6.1-TRIAL1  2000-Dec-18
           5.6.1-TRIAL2  2001-Jan-31
           5.6.1-TRIAL3  2001-Mar-19
           5.6.1-foolish 2001-Apr-01     The "fools-gold" release.
@@ -379,9 +378,8 @@ the strings?).
           5.8.0-RC2     2002-Jun-21
           5.8.0-RC3     2002-Jul-13
 
- Jarkko   5.8.0         2002-Jul-18
-
- Jarkko   5.8.1-RC1     2003-Jul-10     The 5.8 maintenance track
+ Jarkko   5.8.0         2002-Jul-18     The 5.8 maintenance track
+          5.8.1-RC1     2003-Jul-10
           5.8.1-RC2     2003-Jul-11
           5.8.1-RC3     2003-Jul-30
           5.8.1-RC4     2003-Aug-01
@@ -417,9 +415,8 @@ the strings?).
           5.10.0-RC1    2007-Nov-17
           5.10.0-RC2    2007-Nov-25
 
- Rafael   5.10.0        2007-Dec-18
-
- David M  5.10.1-RC1    2009-Aug-06     The 5.10 maintenance track
+ Rafael   5.10.0        2007-Dec-18     The 5.10 maintenance track
+ David M  5.10.1-RC1    2009-Aug-06
           5.10.1-RC2    2009-Aug-18
           5.10.1        2009-Aug-22
 
@@ -436,9 +433,8 @@ the strings?).
           5.12.0-RC4    2010-Apr-06
           5.12.0-RC5    2010-Apr-09
 
- Jesse    5.12.0        2010-Apr-12
-
- Jesse    5.12.1-RC1    2010-May-09     The 5.12 maintenance track
+ Jesse    5.12.0        2010-Apr-12     The 5.12 maintenance track
+          5.12.1-RC1    2010-May-09
           5.12.1-RC2    2010-May-13
           5.12.1        2010-May-16
           5.12.2-RC1    2010-Aug-31
@@ -463,11 +459,11 @@ the strings?).
  Jesse    5.13.9        2011-Jan-20
  Ævar     5.13.10       2011-Feb-20
  Florian  5.13.11       2011-Mar-20
- Jesse    5.14.0-RC1    2011-Apr-20
+
+ Jesse    5.14.0-RC1    2011-Apr-20     The 5.14 maintenance track
  Jesse    5.14.0-RC2    2011-May-04
  Jesse    5.14.0-RC3    2011-May-11
-
- Jesse    5.14.0        2011-May-14     The 5.14 maintenance track
+ Jesse    5.14.0        2011-May-14
  Jesse    5.14.1        2011-Jun-16
  Florian  5.14.2-RC1    2011-Sep-19
           5.14.2        2011-Sep-26
@@ -486,11 +482,11 @@ the strings?).
  BinGOs   5.15.7        2012-Jan-20
  Max M    5.15.8        2012-Feb-20
  Abigail  5.15.9        2012-Mar-20
- Ricardo  5.16.0-RC0    2012-May-10
+
+ Ricardo  5.16.0-RC0    2012-May-10     The 5.16 maintenance track
  Ricardo  5.16.0-RC1    2012-May-14
  Ricardo  5.16.0-RC2    2012-May-15
-
- Ricardo  5.16.0        2012-May-20     The 5.16 maintenance track
+ Ricardo  5.16.0        2012-May-20
  Ricardo  5.16.1        2012-Aug-08
  Ricardo  5.16.2        2012-Nov-01
  Ricardo  5.16.3-RC1    2013-Mar-06