Allow cabal-install to re-install itself on Windows
This is a fairly heavyweight solution, but then it's quite a nasty problem. What we do is when we notice that we're about to install something in place of our own .exe file, we move our exe file out of the way (but in the same dir). Then after we've installed the new exe we call it and ask it to delete the old file (so we do not litter the bin dir with lots of old versions). That requires synchronising between the old and new programs and for the new program to understand a command to do the syncing and deleting of the old program. Lots of Win32 FFI imports. :-( On the plus side it seems to work and is transparent to the user and the rest of cabal-install. In particular the actual file-installation code (which is burried deep within Cabal) does not need to know about the special case of installing over our own exe file.
Showing with 294 additions and 12 deletions