Set initial value of child_pid and masterfd, and don't treat CTRL_C
event when not initialized.
PTY hold mode would not make child process.
Signal handlers treat child_pid initialize status.
Change constant values into symbols.
Enlarge communication buffer size.
Remove some global variable dependency.
Remove some global variable dependency.
Fix comdition check mistake of process-tty-name.
Use zerop instead of eq 0.
Fix indentation.
Add kill-process's advice.
Some signals use subprocess's pgid instead of fakecygpty's pgid.