TLB: comments and a helpful warning.

TLB: comments and a helpful warning.

Nothing big here, but when you have an address that is not in the page table request to be allocated, if it falls outside of the maximum stack range all you get is a page fault and you don't know why.  Add a little warn() to explain it a bit.  Also add some comments and alter logic a little so that you don't totally ignore the return value of checkAndAllocNextPage().