mail/fetchmail: avoid rc.conf overriding daemon interval, many other fixes

Authors: CH = Corey Halpin, MA = Matthias Andree

• fetchmail's rc script now queries the daemon interval from the configuration, and falls back to the rc.conf value if given. [CH]
• Similarly, the logging facility will be taken from the configuration [MA]
• Add documentation to the rcfile's header comments. [MA]
• Drop support for fetchmail_home_prefix in rc.conf, and query the respective users' home directories with getent instead. [MA]
• In the rc scripts, redirect input from /dev/null so it will not ask for passwords. [MA]
• Add support for the typical 12.1 rc.conf ${name}_... keywords. [MA]
• Make script execution easier to follow by simplifying if...else logic. [CH]
• Fix rcscript's exit code to be 1 if one of the per-user calls fails. [CH]
• Add relevant notes to UPDATING. [MA]

PR: 249860
Submitted by: Corey Halpin (maintainer)
Reported by: Chris James (on fetchmail-users mailing list)
Approved by: Corey Halpin (maintainer)