Exhaustively check for unhandled function call errors.

[TravisWhitaker]

I've found lots of things like pointers from malloc/fopen/etc. that aren't checked through the course of adding proper error handling. We should do an exhaustive check for these sorts of things at some point.

[harlanhaskins]

Some kind of xmalloc would be good. perror and exit

[TravisWhitaker]

Using things like xmalloc will make interfacing with things that need to clean up after themselves (e.g. language runtimes) untenable.