mail/fetchmail: mail/fetchmailconf: Update to 6.4.13 [1], fix rcfile bug [2]

Update mail/fetchmail{,conf} to 6.4.13 and fix rc script to work correctly
when root's shell does not include /usr/local/bin in $PATH.

mail/fetchmail passes 'poudriere testport' on both i386 and amd64 under
11.4 and 12.1 for the following configurations:

• Default settings
• Default settings, build as non-root
• ssl=base, GSSAPI_MIT
• ssl=base, GSSAPI_NONE
• ssl=openssl
• ssl=openssl with SSL2 and SSL3 disabled
• ssl=openssl, GSSAPI_NONE
• ssl=libressl
• ssl=libressl, GSSAPI_NONE

mail/fetchmailconf passes 'poudriere testport' on both i386 and amd64 under
11.4 and 12.1 with default settings

Additionally, passes bulk -tC on 12.1-arm64.

PR: 250925 [1]
Submitted by: Corey Halpin (maintainer)
PR: 250691 [2, comments #14, #15]
Reported by: Brian Biskeborn [2], Andrey Kiryanov [2]