Optimizing net related classes

This pull request contains several commits that optimize net related classes. Mainly header parsing and formatting of net messages. The changes are mostly non-critiical. Commit 3c64846 breaks BC (in a non painful way), the commit message explains it's why and how. I think it's worth it.

The attached screenshot shows the xhgui summary, comparing the latest dev branch with the patches proposed here. The benchmark is JSON benchmarks from the TechEmpower framework benchmarks. The only exception here is I didn't enable APC caching.

![bildschirmfoto 2014-05-06 um 23 14 57](https://cloud.githubusercontent.com/assets/29702/2895734/b68c9234-d563-11e3-9bcc-e8f7a38a93ea.png)

Please note that wall & cpu time is not relevant here, it cannot be used for a comparison. Benchmarks must be conducted differently for this of course. However it can be assumed with a lower mem footprint we might get more req/s.