Compatibility:  WIN 3.0+
Expects: AX    1709H
SI:CX desired memory size needed
Returns: DX:AX Largest block of free memory available to clipboard
0000:0000 = error or no memory
Info: This checks to see if a specified amount of data will fit into
the clipboard.  It appears to call the Windows memory manager to
have it rearrange moveable memory blocks to make room for a
specified-size memory allocation.  Equivalent to

Typical usage is to set SI (high word) and CX (low word) to the
size of the data you intend to place in the clipboard.  Call this
fn, and if DX:AX returns with the same or larger value, then its
OK to go ahead with INT 2fH 1703H (put data into clipboard).

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INT 2fH 1709H: See if Data Will Fit in Clipboard