Jiggs as a racial epithet
Trivia section for this movie says:
"In the novel and the earlier version of the film, Seven Days in May (1964), the character played here by Forest Whitaker was named Martin "Jiggs" Casey. The nickname, which in the context of an African-American actor was a racial epithet, was clearly inappropriate and was not used."
Could someone explain to me in what sense is "Jiggs" a racial epithet? I'm not from the States and this is the first time I hear about this, so I'd really appreciate it if someone could clarify this for me. Thanks.