Part1: Functional changes

Backporting upstream changes.
commit a7e1ef858ee82493dd8ad9a76bc9c22fe3b8c05b
Author: Neha Kumari <neha.n.kumari@oracle.com>
Note:
From the upstream patch only the new option binlog_expire_logs_seconds
specific changes are taken.

* Unlike in the upstream patch 'binlog_expire_logs_seconds' does not
  replace the "old" 'expire_logs_days', to preserve backward-compatibility.

* Datatype of 'expire_logs_days' variable is changed to double.

* Default value of 'binlog_expire_logs_seconds=0' similar to
  'expire_logs_days'.

* The purge_time can be specified in days with the micro-day precision.
  Eg:
  expire_logs_days=1 is the same as expire_logs_days=1.000000 to make
    binlog_expire_logs_seconds=86400.
  binlog_expire_logs_seconds=1 is the same as expire_logs_days=0.000012.

* If binary log is disabled and option 'expire_logs_days' or
  'binlog_expire_logs_seconds' used with purge_time > 0 a warning will be
  issued.