Replace 1.18.0.0 with 1.18.0 in 'bootstrap.sh'.

Fixes #1473.
sandbox init: warn instead of dying if there's a cabal-dev sandbox.

Fixes #1472.
'cabal repl': require Cabal version to be >= 1.18.

Fixes #1478.
Merge pull request #1480 from 23Skidoo/issue-1478

'cabal repl': require Cabal version to be >= 1.18.
Wording.
'cabal-sdist': include extra-doc-files.

Fixes #1477.
Don't allow 'sandbox-config-file' in '~/.cabal/config'.
Reconfigure if 'cabal.config' was changed.

Fixes #1485.
Add a FIXME.
Add a workaround for issue #1463.
Reconfigure on modified 'cabal.config' even when there's no sandbox.

See #1485.
Depend on Cabal 1.18 instead of 1.17.

Avoids potential conflicts with old Cabal snapshots.
Change an error message.

See #1488.
Merge pull request #1469 from 23Skidoo/issue-1463

Add a workaround for issue #1463.
Initialise 'configInstallDirs' properly when loading sandbox config.

Fixes #1482.
Bump version number of cabal-install to 1.18.0.1