[BASH] Refactor .bashrc.

Signed-off-by: Wei-Chung Wen <morisato3711@gmail.com>
[VIM] Enable wildignorecase only with VIM >= 7.0.4.

Signed-off-by: Wei-Chung Wen <morisato3711@gmail.com>
[BASH] Fix prompt for Git on Mac.

Signed-off-by: Wei-Chung Wen <morisato3711@gmail.com>