Issue #2504815 by neclimdul, phenaproxima, mikeryan: d6 to d8 migration throws integrity contraint warning with duplicate file paths

Issue #2534012 by phenaproxima, hussainweb, mikeryan: Move module-specific migration support into the file module

Issue #2503861 by phenaproxima, benjy, alexpott, mikeryan: Migrate file_managed table to file entities

Issue #1897058 by disasm, rteijeiro: Replace "boolean" with "bool" when used as param/return/var type

Issue #2121299 by andypost, bdone, benjy, penyaskito, chx, claudiu.cristea, damiankloip, gregboggs, InternetDevels, jessehs, jhedstrom, marvil07, mikeryan, pcambra, Xano, YesCT, axoplasm, kgoel, dclavain, jeckman, alvar0hurtad0, Drupali, fastangel, gloob, jhedstrom, joshtaylor, mpgeek, alexpott: Migrate Drupal 6 to Drupal 8