Failing test-case for sandbox add-source regression.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
-Wall police.
Check that sandbox exists before running 'sandbox delete'.
Only call 'listBuildTreeRefs' when actually needed.
It's safe to add ignored add-source deps to the timestamp file.

And should be faster.
Print the "Cache updated" message from a single place.
Force-update the cache in 'add-source'/'remove-source'.

Fixes #2060.
GHC issue #8825 was fixed in 7.8.4.
Remove all references to Data.Version.versionTags

Avoids deprecation warnings when versionTags is deprecated in GHC 7.10
(GHC ticket #2496)
Merge pull request #2188 from thomie/versionTags

Remove all references to Data.Version.versionTags
-Wall police (Win64 edition).
Fix 'cabal clean' on Windows for 'build-type: Custom'.

Fixes #1863.
Revert 97c6a72984931f4ccf628736024d3459a033af6c.

That commit prevented 'sdist' from printing distribution quality warnings.
'writeFileAtomic': use default permissions.

Fixes #2078.
Add packageKey to the Cabal Paths module.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>