Executes command for up to "time" seconds.

If program works more that "time" seconds, timeout kill()'s it.
After kill(), optionally second command is started.

Example usage:

Executes ls -al for up to 20 sec.
./timeout 20 'ls -al'

Executes top for 10 seconds:
./timeout 10 top

Executes top for 10 seconds, then executes ls -al:
./timeout 10 top 'ls -al'