[BUGFIX]: Added error handling for import_sys_env_var(), added code to use default variable if the system can't supply the desired variable from the system environment.
[FEATURE]: Added terminal-control grabbing and process group initialization. Shell is now stand alone (can be used as a login shell). Added pid/pgid/terminal/is_interactive/tmodes to shell_t.
[CLEANUP]: Added semicolons to SET_SIGNALS_SHELL and SET_SIGNALS_PROC calls.