Hey I just had a look at `close` and it doesn't do any error checking.
The following program results in a memory corruption:
var f = open("hello.txt", fmWrite)
f.write("test\n")
f.close()
f.close()
This leads me to think that I should set the pointer to `nil`. Closing nil results in a segfault, which is probably(?) less dangerous than double-free corruption. I'm not an expert in that area.
