Trailing newline.
A fix for my previous fix for 'getSourceFiles'.

Apparently, lazy I/O was involved after all. 'openFile' instead of 'withFile'
was deliberate - see the use of 'unsafeInterleaveIO' in
'packageIndexFromCache'. Fixed by adding a strict version of 'getSourceFiles'.
Revert the timestamp checks back to (>=) from (>).
Work around the low clock resolution problem of 'getModificationTime'.

See http://hackage.haskell.org/trac/ghc/ticket/7473 .
Unbreak 'tryCanonicalizePath' on Windows.
Mark the '.cabal-sandbox' dir as hidden on Windows.
Merge pull request #1301 from 23Skidoo/getmodtime-and-other-fixes

Workaround for low clock resolution problem of `getModificationTime` + other fixes
Add a TODO.
Add a rudimentary README for 'cabal-install/tests'.
Better error message.
Be more strict when parsing 'cabal.config'.

In rare cases (when 'cabal-dev -s .' was used) its 'cabal.config' could conflict
with our 'cabal.config'.
Refuse to create a sandbox if there's already a cabal-dev sandbox.

Also improve a message that gets printed when we find a cabal.config created by
cabal-dev.
80-col violations.
Add a comment about the setup exe cache.
Fix 'getModTime' with base < 4.5.
Include PackageTests files into the tarball.
Add tests/README to extra-source-files.
Fix the 'index.cache' timestamp check.

Since we're using 'unless' here, we should use (>) instead of (>=).
Whitespace.
Make some error messages more user-friendly.

Fixes #1304, #1007.