mfsRamGetFreeSize


Format:	s32 mfsRamGetFreeSize(void)
Arguments:	None
Return value:Size of free space (a negative value is an error)
Function:	Obtains size of free space
Description:	This function obtains the size of free space on the disk.  It calculates and returns the total block size of all unused blocks, in bytes.

Main errors:
	MFS_ERR_NOTMFSDISK Not an MFS-format disk
			The disk ID's disk use is not 1, or the header is different.
	MFS_ERR_VERSION	Different version disk 
	MFS_ERR_PROTECT	Write protected
			The medium is volume protected.