The minimum number of lines of any window.
The value has to accommodate a mode- or header-line if present.
A value less than `window-safe-min-height' is ignored. The value
of this variable is honored when windows are resized or split.
Applications should never rebind this variable. To resize a
window to a height less than the one specified here, an
application should instead call `window-resize' with a non-nil
IGNORE argument. In order to have `split-window' make a window
shorter, explicitly specify the SIZE argument of that function.