database install

This changes how the SCOPE_OF_INSTALLATION variable is used to provide
an alternate way of running bootstrap.sh which can install
cabal-install to a separate prefix and package database without
altering the user's package database or using it. The idea with this
is to improve the repeatability of automatically installing ghc, cabal
and other haskell independently of the current standard installation
or the user's main package database.

Usage example:

ghc-pkg init /home/jake/test_cabal/
SCOPE_OF_INSTALLATION='--global --package-db=/home/jake/test_cabal/packagedb' PREFIX=/home/jake/test_cabal/prefix ./bootstrap.sh

If you don't override the SCOPE_OF_INSTALLATION variable, bootstrap.sh
works as before.

tarballs if these tarballs are already present.

NETWORKURI_VER_REGEXP should be NETWORK_URI_VER_REGEXP

So that the 'install_from_tarball' build bot step doesn't try to use the old
1.21 snapshot that comes with GHC HEAD.

Fixes #2009.

Fixes #1994 (hopefully).

Fixes #1902.

This reverts commit 41678698.

See discussion in #1796.

https://github.com/haskell/cabal/issues/1796

(The current https://hackage.haskell.org/ SSL certificate does not have
identity validation, so `--no-check-certificate` must be passed to `wget`
in order for it to fetch without error.)

Mikhail Glushenkov authored Apr 16, 2014 and tibbe committed Apr 17, 2014

(cherry picked from commit a63871b7)

Conflicts:
	cabal-install/bootstrap.sh

Should fix Travis failures.

Prior versions didn't include an upper bound on network and might
therefore cause build failures as the relativeTo function was changed
in network-2.4.0.0.

Hackage 2 doesn't support byte ranges at the moment, which makes curl exit with
error if there's an incomplete tarball present. Fixes #1675.

There were three errors in CC detection:

1. The wrong variable was used in the for loop.

2. The selected CC was checked for existence and execute perm,
   but instead of the full path to the executable just the basename
   was passed to test -x.

3. The info log message accidentally printed the value of CC.

Downloading was failing with curl which seems
not do http redirect by default.

This change simple updates the urls from

Hackage 1's http://hackage.haskell.org/packages/archive/$PKG/$VER/$PKG-$VER.tar.gz to
Hackage 2's http://hackage.haskell.org/package/$PKG-$VER/$PKG-$VER.tar.gz

which makes curl happy and downloads work again.

cabal.git 7f9c23d8 fails when configuring network:
checking whether the C compiler works... no

To fix that, update network version to 2.4.2.2.

See #1634.