Add missing header guards

[bog-dan-ro]

Use #pargma once everywhere.

[alvieboy]

I am sorry, but I disagree with #pragma usage, which is a non-portable compiler extension. The most portable and standartized way is to use ifdef/define/endif as already present in the code. If you did find missing guards, then I'll gladly accept ifdef/define/endif where they are missing (and eventually C++ extern statements if applicable).