This commit adds open and close syscalls to the kernel, and adds matching wrappers to libc.
No read/write support, so file descriptors are kind of useless for now.
getpwent, getpwnam, getpwuid... they may have been a pain to implement but once they work they're awesome :)
Right now passwords are stored in plaintext in the world-readable passwd file, which is not good.
But I don't have any sort of hashing implemented so it'll stay that way for now.
