add pkgls functionality for pkgbuild

In a similar manner to previous conditionals, this forks pkgls to allow
for the same verbose output displaying the bill of materials that was
used with the bundle pkgs packagemaker generated, which for pkgbuild
utilizes pkgutil’s —bon option.
Merge pull request #49 from unixorn/add_lsbom_to_pkgbuild

add pkgls functionality for pkgbuild