bigint' fails on windows.

Visual Studio does not take into account some x86 hardware limitations
which leads to incorrect results when converting large DOUBLE values
to BIGINT UNSIGNED ones.

Fixed by adding a workaround for double->ulonglong conversion on
Windows.


include/config-win.h:
  Added double2ulonglong(double) function implementing a workaround for
  broken double->ulonglong conversion on Windows/x86.
include/my_global.h:
  Define double2ulonglong() as a simple typecast for anything but
  Windows.
mysql-test/r/type_float.result:
  Added a test case for bug #27483.
mysql-test/t/type_float.test:
  Added a test case for bug #27483.