Fixes #1823.

cabal upload: support package candidates

The message now includes a link to the package page and says
whether the package was uploaded as a candidate or not.

When uploading package candidates, the hackage server will return 204 responses in some cases.
The upload was still successfull in that case though.

We now also display warnings that the hackage server gives when a package is uploaded.

This adds support for uploading package candidates by introducing a new flag to `cabal upload`,
--candidate. With this flag, `cabal upload` will upload all supplied tarballs as package candidates.
If combined with `--documentation`, the flag can also be used to upload documentation for a package
candidate to hackage.

Fixes #3418

Add (optional) tracetree support into the cabal executable

Add an AUTHORS file and simplify copyright notices.

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Also rename CONTRIBUTORS to AUTHORS, which seems to be more standard.

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Report process output decoding errors in context

Not all the exception handling, just for the case fixed by the previous
patch.

Turns out of course that this is sensitive to the locale encoding, so we
just skip the test when the localeEncoding is not UTF-8.

Adjustments for what deps we pick for legacy Setup scripts in new-build

Add a lower bound of >= 1.18. Also improve the related comments.

Using >= 1.18 since we currently have problems working with 1.16 as that
version lacks support for named build targets. We ought to fix working
with older versions though.

Add transformers and old-time, and for ghc-compatible compilers also add
ghc-prim and template-haskell.

Have to double check if the old-time dep needs to be conditional, e.g.
on ghc version.

It turns out that in rawSystemStdInOut any IO errors, including text
decoding, occurring while collecting the output (stderr or stdout) do
not get reported immediately, but only later if/when the output is
consumed. This is because the exceptions happened in the threads forked
to force the output, but if the main thread looks at the output later
then the exception is reported again.

This leads to very confusing results. In particular we had a case where
the configure process did not fail until writing out the LocalBuildInfo
because that was the first point that forced the output. So the distance
from when the exception really occurred and the fact that the exception
message does not include the name of the program run means that this is
then a pain to track down.

This patch makes sure that any exceptions arising from forcing the
program output occur immediately and with an error message that includes
the name of the program in question.

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

Unfortunately, it was too difficult to factor out the common code
between ProjectBuilding and Install.

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

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

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

Move solver types to Distribution.Solver.* namespace