Pkg 1.9.4

What's Changed

• Backports release 1.9 by @IanButterworth in #3595
• [release-1.9] Backports for 1.9 by @IanButterworth in #3599
• [release-1.9] Backports for 1.9 by @IanButterworth in #3619
• [release-1.9] Backports 1.9 by @IanButterworth in #3647
• [release-1.9] 1.9 backports by @IanButterworth in #3681
• Backport 1.9: remove recompilation dependency check in Pkg.precompile (#3696) by @KristofferC in #3697

Full Changelog: v1.9.3...v1.9.4