abuild: maintainer field check is not RFC822-compliant

*[A-Za-z0-9]*\ \<*@*.*\> glob doesn't match the RFC:

     mailbox     =  addr-spec                    ; simple address
                 /  phrase route-addr            ; name & addr-spec
     phrase      =  1*word                       ; Sequence of words
     word        =  atom / quoted-string
     atom        =  1*<any CHAR except specials, SPACE and CTLs>

(sections hand-picked to show the issue)

in our case, phrase is defined as [A-Za-z0-9], which doesn't allow for atom from the RFC and causes errors on valid emails like such:

# Maintainer: Jeremy O'Brien <neutral@fastmail.com>