WinXP r5588 pak64 - Lower/Raise land tool has inconsistent behavior

[IgorEliezer]

Simutrans sometimes forgets to reset the variable that stores the "target" depth between the draggings.

For example, activate Lower land (Key D), click on a tile at Z = 2, drag, you'll get a terrain at Z=1.

Then, without exiting the Lower land, click on a tile at Z = 0 and drag, you'll get a terrain at Z = -1. That's okay.

Now, without exiting the Lower land click on a tile at Z = 2 and drag, you'll get a terrain at Z = -1.

[Dwachs]

Should work correctly with r5619.

The flag that indicates 'tool is used for dragging' was not correctly reset if using the lower-tool to lower land to sea-level.

[IgorEliezer]

Thank you.