.emacs: use setq not setq-default for local settings like tab-width and indent-tabs-mode

The setq-default was setting the mode globally, so, if I opened a .go
file, setq-default would set tab-width to 4 globally, then when I
opened .sh file, my tab width is 4.  Go is a special case.  I use
tab-width 4 there because it is all tabs, no spaces.