Problem: using null microsecond part (e.g. "YYYY-MM-DD HH:MM:SS.0000") 
in a WHERE condition may lead to wrong results due to improper
DATETIMEs comparison in some cases.

Fix: as we compare DATETIMEs as strings we must trim trailing 0's
in such cases.


mysql-test/r/innodb_mysql.result:
  Fix for bug#47963: Wrong results when index is used
    - test result.
mysql-test/t/innodb_mysql.test:
  Fix for bug#47963: Wrong results when index is used
    - test case.
sql/item.cc:
  Fix for bug#47963: Wrong results when index is used
    - comparing DATETIMEs trim trailing 0's in the 
  microsecond part.