Fix some warning

[Yvon TANGUY]

I have fix some random warning, during a boring raining day...

It include some of theses warnings:
Wmissing_braces
Wreturn_type
Wsign_compare
Wuninitialized
Wunused

It compile, so it's perfect !

OS: Ubuntu GNU/Linux 12.04 64bits
Panda3D: CVS Head (main?) 1.8.0+

Note for after: there is a ugly thing to fix in the Pyhon glue code:
panda3d/built/include/py_panda.h:172:55: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

But for me it is a mess out there, I do not understand the code enough to clean it.

[Josh Enes (joshenes)]

Some of these changes look dangerous, fixing warnings simply by commenting lines out.
It might be worth reviewing the patch, but carefully.

[rdb (rdb)]

Most of the lines he commented out were unused variables. Still, there's a lot in there I'm not sure about, and things that would probably break other systems. I'll look into it when I have the time, but to be honest it's not high on my todo list.