Wait until function, class, directory, file or variable exists

USAGE
waited = wait_for_existence(name,type,pause_time,max_time)

INPUT
- NAME: name of the function, class, directory, file or variable (must be a string)
- TYPE: 'builtin', 'class', 'dir', 'file' or 'var'
- PAUSE_TIME: amount of time to wait in the pauses (in secs)
- MAX_TIME: maximum amount of time to wait (in secs)

OUTPUT
- WAITED: 0 (if NAME exists) or 1 (if NAME does not exist and MAX_TIME has been elapsed)