mailto in exector control should allow any string

Any string should be allowed in mailto.

"operations <ops@example.com>"

OR

"infosec <infosec@example.com>, pager <pager@example.com>"

Any string that is legal in a mail user agent's To heading should be permitted in Cfengine's mailto variable. Mail programs are excellent at parsing email addresses. Cfengine 3 should not be burdened with this.

See discussion:
https://groups.google.com/forum/#!topic/help-cfengine/ujsgOi9JBsU