Only grab 4mb page when pse is set

This is a really obscure issue that I just been poking at for fun.

According to the Intel manual, without CR4.PSE=1, the Pentium will always use Intel 486-compatible (4-KB) paging, regardless of the setting of the PDE.PS bit (http://www.rcollins.org/ddj/May96/May96.html). Of course, there is no way of telling whether pse is set during file mode, so in that case we are stuck with whatever the pde says.