Revert "replace Gem::Format.from_file_by_path with Gem::Package.new"

This reverts commit 150489b91a9d12332a2e06398b0f400092987248.

Gem::Package.new exists in rubygems-2.x but ruby-1.9 uses rubygems
1.8.x. I was using rubygems-2.x on my laptop instead because I should
have run

rvm rubygems latest-1.8

to make rubygems-1.8.x the default, which caused all this confusion
bump version 1.78.0