Re-add 'classP' with a compatible implementation and a deprecation notice
Provide deprecated backward compatible implementation to 'equalP'
Catch some typos
Fix below warning by including "unistd.h" also

exec_signals_prepare.c:26:5: warning: implicit declaration of function 'execv' is invalid in C99
      [-Wimplicit-function-declaration]
    execv(argv[1], argv+1);
    ^
1 warning generated.