Edward Z. Yang authored Feb 11, 2017 and Edward Z. Yang committed Feb 12, 2017

- Report all reexport errors, not just the first one
- Give more information about how the modules are different
- Add quotes and prettify the foramt
- Preserve spaces when reporting errors

The new message looks like this:

Problem with module re-exports:
  - Ambiguous reexport 'Data.Map'
    It could refer to either:
         'containers-0.5.6.2-59326c33e30ec8f6afd574cbac625bbb:Data.Map'
         brought into scope by the build dependency on containers
      or 'containers-dupe-0.1.0.0-2AdbRP7BsOEKELRWSQejuE:Data.Map'
         brought into scope by the build dependency on containers-dupe
    The ambiguity can be resolved by qualifying the
    re-export with a package name.
    The syntax is 'packagename:ModuleName [as NewName]'.
  - The module 'Missing'
    is not exported by any suitable package.
    It occurs in neither the 'exposed-modules' of this package,
    nor any of its 'build-depends' dependencies.
  - The module 'Private'
    is not exported by any suitable package.
    It occurs in neither the 'exposed-modules' of this package,
    nor any of its 'build-depends' dependencies
setup: Configuration failed

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