Revert "Handle read(n) returning nil"

This reverts commit 578cb637594d32b86322be29205329d700ad75ca.
Revert "Don't raise in mach_data so the debugger doesn't catch it"

This reverts commit 4f8a3e2113c2e7b88600ff6371f9f70579c55509.
Revert "Allow debugging patch failures"

This reverts commit 988601624568a951d86bd00cf441d18681b4b500.