vfs: don't map CoW source page writeable when copying data on write, don't let multiple traps handle a CoW write at the same time on the same CPU.
x86: flush TLB for all cases (not just 'marked swapped') in VirtualAddressSpace::doMap, and do a TLB flush in setFlags too. Fix the location of the flush for doUnmap too.

This fixes Pedigree under KVM.