Remove the self-upgrade check.

Fixes #2089.
Add a right-biased variant of 'NubList'.
GhcOptions: use `NubListR` where appropriate.

Some Cabal API clients apparently use `foldl mappend` on large lists of
`GhcOptions` records. Fixes #2110.
80-col violations.
Merge pull request #2111 from 23Skidoo/ghc-options-union

GhcOptions: use `NubListR` where appropriate.
Remove support for Hugs and NHC98.

Fixes #2130.
Merge pull request #2090 from 23Skidoo/no-update-check

Remove the self-upgrade check.
Merge pull request #2168 from 23Skidoo/remove-hugs-and-nhc-support

Remove support for Hugs and NHC98.
'parseInstalledPackageInfo': silently ignore 'hugs-options'.

Fixes #2171.