CopyFile: Check for file existence instead of catching all exceptions
CopyFile: Add copyFileChanged and comments
Implement '--enable-library-stripping'.

Fixes #1622.
Rename 'findPackageDesc' to 'tryFindPackageDesc'.

Make 'findPackageDesc' return an 'Either'.
'cabal repl': when there's no .cabal file, just start ghci.

Fixes #1554.
Add function that only copies on change

This is useful when implementing e.g. re-linking avoidance.
Fix doc to refer to correct copyFile function name
Merge pull request #1607 from 23Skidoo/repl-no-project

'cabal repl': when there's no .cabal file, just start ghci.
Implement the 'require-sandbox' option.

Fixes #1596.
Merge pull request #1625 from 23Skidoo/require-sandbox

Implement the 'require-sandbox' option.
Merge pull request #1623 from 23Skidoo/library-stripping

Implement '--enable-library-stripping'.
Fix some violations of Monoid laws.