clean up stack manipulation of error handler function in pi_lua_dofile
extract function pi_lua_loadfile from pi_lua_dofile
don't try to get a traceback for a syntax error in pi_lua_dofile
run a file ~/.pioneer/console.lua when initialising the console

This file can be created by the user to put useful things into the console
environment. For example, importing game API modules and defining helpful
functions or values.

Errors in console.lua are reported in stderr, but do not trigger a full
redscreen panic.
fix references to 'autoexec.lua' (should be 'console.lua')
remove unnecessary warning about Lua file paths that begin with '['
Merge remote-tracking branch 'johnbartholomew/console-autoexec'