default global install on windows is a problem

[duncan]

Lots of windows users have problems installing things globally. Some are using multi-user systems. More are using Vista where it seems that even when they are running as administrator they cannot install files in C:\Program Files\.

We should revisit the decision to install globally and see if we cannot find a default that works better. Failing by default is bad.

We may also want to try to improve the checking beforehand to check if we would have permissions to write into the target directories. If not we can fail at configure time rather than waiting until install time and failing ungracefully.

This needs someone who knows and cares about windows. Particularly for the Vista aspects.

[duncan]

See #320 for an example of what happens on Vista and trying to do global installs, even when the user has admin access.

Then if they do do a global install as administrator they get #454, where the permissions are such that only the administrator can run the program.

[duncan]

I'm convinced the only sensible thing to do is to default to per-user installs and to reject --global installs unless we were launched with elevated privileges (meaning from within a elevated privileges console window).

Providing a way to elevate privileges at just the right time is just too hard on Windows.

See #320 comment 9.

[duncan]

So cabal-install-0.8.2 will do per-user installs by default.