SYNOPSIS
    string add_a (string text)

DESCRIPTION
    If <text> does not start with "a " or "an ", the appropriate
    article is added. Result is the possibly modified string.

EXAMPLE
    add_a("cart")   --> "a cart"
    add_a("apple")  --> "an apple"
    add_a("a tree") --> "a tree"

SEE ALSO
    strip_a(SEFUN), strip_article(SEFUN)