Inject packages only once per file

- Injecting a file into the local CPAN mirror was done once per
  module in a distribution instead of just once per distribution
  package file. This made injecting large packages like Date-Manip
  (972 modules), DateTime-Locale (469 modules), and DateTime-TimeZone
  (421 modules) an eeenie-meenie-teeny little-bit faster. :)