Set CURLOPT_SSL_VERIFYPEER to TRUE (refs #3196)

To add your own trusted certificate (on Debian and derivatives):
- copy your cert's file (e.g. `www.example.net.crt`) into
  `/usr/share/ca-certificates`
- edit `/etc/ca-certificates.conf` and append a line with your cert's filename
  (e.g. `www.example.net.crt`)
- run `update-ca-certificates`
Merge pull request #91 from eguaj/1.4-A3196

Set CURLOPT_SSL_VERIFYPEER to TRUE (closes #3196)