Heads-up: code style tweaks applied

[McDutchie]

A few of the archaisms in the code style finally got on my nerves, particularly because they were used so inconsistently. See 427ea54. As of now the code uses standard NULL pointers instead of NIL(type*), (type*)0 or NiL, and return foo; instead of return(foo);. I've also eliminated the register keyword.

ping @JohnoKing, @hyenias

[JohnoKing]

The removal of the register keyword is very welcome, primarily because debug builds no longer need -Dregister= added after -O0. To be specific, GCC is prone to optimizing variables created with the register keyword, even when compiling with -O0. Stacktraces as a result become less useful, because variables of interest may be optimized out when register is used.

[phidebian]

Thanx tons for register removal, I was on the same course as @JohnoKing using -Dregister= having variable optimised out at -O0 was super anoying.

Regarding return() I am more reserved, all my project do used return() because it does't hurt, and allow some hacks like insrtumenting return's occurences, do at_return() things, etc... specially interesting on legacy code, with big spaghetti function and a lot of return points... hacking may define a macro return() (log stuff etc...)