RFC : Load tests

This patch is a starting point to add more load tests. 

Currently it has the following:

- 100000 socket connect/disconnects

- Sequential send of 1GB of data between two Julia processes

- Bidirectional send/recv of 1GB of data between two Julia processes

A couple of tests for memory leaks. Currently Linux only. 

Primes a test function, and gets the difference in vmsizes before and after a run. Prints a warning if the difference is more than 1000 KB

Let me know of any more tests we can add. And if Base if not a good place for these tests I'll move it into its own package. 

### TODO
- Add timing information 
- Print other system resource usage.

Any other ideas?