extract current timestamp fetching
change interface of getting current time-stamp
bugifx: need instance variable for storing errno
store overtime boundary time-stamp in time_t variable
renamed boundary timestamp for stopping program to tstamp_onstop_*
implements program wait and overtime stopping
bugfix: fix return type
add prototype of wait_program()
extract program running part for tests with same parameter for run_program
bugfix: waitpid() returns pid_t
add test for blocking wait on empty program
extract verification code for empty program
save finish timestamp
also checks finish-time
add test for nonblocking wait
implements stop program function