bug#36817: Guix Download Fails When SSL_CERT_DIR is a Colon-Separated Path

[Katherine Cox-Buday <cox.katherine.e@gmail.com>]

I was receiving X.509 certificate errors when attempting to run `guix
download`. After investigating, I found that it was because my
`SSL_CERT_DIR` environmental variable had two paths separated by a
colon. The two paths were actually the same. After removing the second
path, `guix download` began working again.

Wondering how the duplicate paths came to be, I discovered that
`${GUIX_PROFILE}/etc/profile` had two exports defined for
`SSL_CERT_DIR`. I discovered this was because I had both openssl and
libressl installed (if memory serves, I needed openssl for some
development task that relied on an idiosyncrasy of openssl). Removing
openssl removed the duplicate entry.

I think there may be two bugs:

1. `guix download` needs to respect colon-separated paths.
2. The profile mechanics in Guix should probably have some way to check
   if they're redefining the same thing before placing things in `etc/profile`.

Thank you to everyone for all of your hard work, and for Guix.

-- 
Katherine