community/heirloom-doctools: avoid conflicts with common packages

The heirloom-doctools provides several small binaries which are intimately tied together. Unfortunately, these binaries are also provided by other common and packages (e.g. coreutils, util-linux-misc and groff). For this reason, it was previously not possible to have, for example, util-ilnux-misc and heirloom-doctools installed simultaneously.

Since the aforementioned packages are quite popular this is a common annoyance. To workaround this issue, install the heirloom-doctools binaries and man pages to non-standard directories and provide a /etc/profile.d configuration file to add these directories to the PATH and MANPATH.

This approach is also taken by other downstream packagers [1].