Interface files lack a checksum
Motivation
I've been debugging spurious segfaults while loading interface files (.hi). It turned out I somehow managed to sed some strings in these files... leading to crashes in mkFastString (because the length of the string changed)...
Proposal
It would be good to add a checksum to interface files. Just storing and checking the expected file size would already have avoided the segfault. A CRC32 could be useful too.