S9 LIB  (string-prefix=? string1 string2)     ==>  boolean
        (string-prefix-ci=? string1 string2)  ==>  boolean

Return #T when STRING2 has a prefix of STRING1 and otherwise
return #F. STRING-PREFIX-CI=? performs the same operation, but
ignores the case of the strings.

(string-prefix=? "foo" "foobar")  ==>  #t
(string-prefix=? "foo" "fubar")   ==>  #f
