Update water plane code with float calculations (slower but easier to handle).
When watermode is set to 3:
bglayer blahblah... {watermode} {beginsize} {endsize} {perspetive} ....
beginsize and endsize are multplier of the top and bottom size. Perspective specify whether z depth effect should be corrected: 0=no effect(default), 1=perspective&tile, 2=perspective&stretch...
Authored by: utunnels 2011-09-21
Parent: [r3461]
Child: [r3463]
