Require bundler >=1.5.0 and add back x64_mingw and mingw to the tzinfo-data dependency.

This fixes #278.

Remove an unnecessary //i flag while at it.
Merge branch 'fix-bundler-platforms' of https://github.com/knu/huginn into knu-fix-bundler-platforms
add an error when bundling if bundler is older than version 1.5
Merge branch 'master' of github.com:cantino/huginn