Fix almost all the warnings in the Linux Port

[AndoniZubimendi]

This commits fixes almost all the warnings while compiling in my Arch Linux (Gcc 4.6.3 / QtCreator 2.4.1 - Qt 4.8.0).

There are different warning fixes:

• signed/unsigned comparisons
• type punned aliasing
• Uninitialized values
• non void functions not returning a value
• unused parameters

And 2 errors (or I think so):

• In GPD/XDBF.cpp, function DeleteEntry, you have 2 asignations inside an if, I guess they are comparisions
• In gpduploader.cpp, sendRequest the "if (deleteGPDs)" should have curly braces to do what the indentation expects the code to do.

Awesome work. Let me know if you want me to change something

[landaire]

Looking over these changes now! Thanks, Andoni.