InstallShield overwrites existing Sybase files

[CR #402532]

InstallShield overwrites any existing file with the same name.

To protect against loss of data, save a copy of the %SYBASE%\SYBASE.BAT file before installing SDK.

WARNING! Installing SDK 15.0 on the same machine as any ASE release prior to 15.0 prevents the earlier version of the server from booting.