Only compare branches as versions in the policy to sort packages, but not in the solver, fixes #1817
Remove unused variable $version from RootPackageLoad::load

$version is not referenced anywhere past the removed declaration.
Remove unused variable $valid from ConfigValidator::validate
Remove unused variable $dialog from RequireCommand::configure

I traced the get and getHelperSet to Symfony's Console\Command and Console\Helper\HelperSet, and there was only stored variables being retrieved (no actions being done that'd require these functions to be called).
Add class property Compiler::$version

Compiler::$version is referenced within compile, addFile, and getStub
Merge pull request #1926 from Adduc/patch-1

Remove unused variable $version from RootPackageLoad::load
Merge pull request #1928 from Adduc/patch-3

Remove unused variable $dialog from RequireCommand::configure
Merge pull request #1929 from Adduc/patch-4

Add class property Compiler::$version
Merge pull request #1927 from Adduc/patch-2

Remove unused variable $valid from ConfigValidator::validate
Merge pull request #1922 from Seldaek/matchbranches

Only compare branches as versions in the policy to sort packages, but not in the solver, fixes #1817