Silence conversion warnings from malloc arguments

[ZedThree]

Mostly just add an explicit cast when calling malloc and its variants. Sometimes instead change the type of a local variable if this would silence multiple warnings.

Silences more than 300 warnings on GCC.

[DennisHeimbigner]

Are the castings of c/malloc necessary?
I thought that assigning a void* value to an arbitrary pointer was ok
in C.

[ZedThree]

Yes, implicit conversions between void* and other pointers are valid in C and don't generate warnings, so I've not touched the return value, this is just casting the argument(s) which should be size_t. Apologies if that wasn't clear from the description.