Fix bug in power distribution (Generic and Wooden Pipe)

TileGenericPipe.java:
- fixes not calling powerRequest of IPowerReceptor-Pipe

PipePowerWood.java:
- fixes exploding pipes directly behind of a wooden pipe if no power-consumer exists, instead it will only extract the power amount which is requested by the consumers

see:

![2013-03-04_17 59 50](https://f.cloud.github.com/assets/656249/226474/032f7d26-8633-11e2-833b-57616c14f9ca.png)