emacs: Add toggle-tab-width function.

Makes it easy to switch tab-width betwee 2, 4, and 8 spaces by pressing
the F4 key.
emacs: Remove safe-local-variable-values from custom.

These conflict with some c-mode styles.
emacs: Use c-styles for C indentation.

Added 'troth' and 'linux-troth' c-styles to make it easier to switch
between styles. Especially useful for kernel work.

Tab width and indent-tabs-mode are no longer set in my-c-mode-common-hook.
It's better to set these in specfic styles.

Tab width is no longer set globally. Best to set it when needed.
Remove old lhn cruft.
Remove emacs settings from Xresources.

These are not needed since they're done in the .emacs files.
emacs: Fix frame creation.

Tweak .emacs setup for background color, font and geometry so new frames are
created consistently (i.e. all frames are created using the same defaults).