The naive spinlock was not nearly enough to protect kmalloc from
reentrancy problems.
I don't want to deal with coming up with a fancy lock for kmalloc
right now, so I made an InterruptDisabler thingy instead.
It does CLI and then STI iff interrupts were previously enabled.
- putch syscall now directly calls Console::putChar().
- /proc/summary includes some info about kmalloc stats.
- Syscall entry is guarded by a simple spinlock.
- Unmap regions for crashed tasks.
