numbers into char fields" and bug #12860 "Difference in zero padding of
exponent between Unix and Windows"

Rewrote the code that determines what 'precision' argument should be
passed to sprintf() to fit the string representation of the input number
into the field.
We get finer control over conversion by pre-calculating the exponent, so
we are able to determine which conversion format, 'e' or 'f', will be
used by sprintf().
We also remove the leading zero from the exponent on Windows to make it
compatible with the sprintf() output on other platforms.


mysql-test/r/insert.result:
  Added test cases for bug #26788 and bug #31152.
mysql-test/t/cast.test:
  Removed --replace_result, since the result is now correct on Windows.
mysql-test/t/insert.test:
  Added test cases for bug #26788 and bug #31152.
mysql-test/t/type_float.test:
  Removed --replace_result, since the result is now correct on Windows.
mysql-test/t/variables.test:
  Removed --replace_result, since the result is now correct on Windows.
sql/field.cc:
  Rewrote the code that determines what 'precision' argument should be
  passed to sprintf() to fit the string representation of the input number
  into the field.
  We get finer control over conversion by pre-calculating the exponent, so
  we are able to determine which conversion format, 'e' or 'f', will be
  used by sprintf().