generate CURRENT_PACKAGE_KEY macro in `cabal_macros.h`
Do not fail when the setup executable does not exist when checking
for the windows clean hack.

This would cause exceptions when using a cached setup executable,
making parallel builds on Windows completely unusable.
Merge branch 'master' into 1.22
bootstrap.sh: don't run Haddock on network-uri-2.5.0.0

That package doesn't have any modules and Hadddock chokes.