[RFC] misc2.c -Wconversion changes

First go at helping out. Hopefully misc2.c goes away, but in the mean time I fixed up the one method in it that had -Wconversion errors, per #567.

xmallocz zeroes the string at the end, no need to double up on nulling it.

After looking, it seemed like a cnt of int was adequate, no callers used larger sizes. Still, should it be size_t?
> I know that using `char` here works the same as `uint8_t`, however it would be nicer to use an unsigned type as that's what `getc` returns inside the `int`.

I'm still trying to deduce what you mean by "nicer"--sorry!  Is your underlying argument here is that it could prevent a subtle bug because a platform could (theoretically) use a different mechanism for representing numbers, which could cause the character read to be wrong?  Or is the argument really just that it is more consistent with what's happening under-the-hood?

I only ask because avoiding casts is nice, since they can hide bugs.  I would've swung the other way here said it should be `char *`.  So I'm trying to understand your philosophy about this so that I can either amend my vision or yours. :-)