Set default value of various coding systems to CODING-SYSTEM.
This sets the following coding systems:
o coding system of a newly created buffer
o default coding system for subprocess I/O
This also sets the following values:
o default value used as `file-name-coding-system' for converting file names
if CODING-SYSTEM is ASCII-compatible
o default value for the command `set-terminal-coding-system'
o default value for the command `set-keyboard-coding-system'
if CODING-SYSTEM is ASCII-compatible