Drop messages from non-leading Masters in the scheduler driver.

Review: https://reviews.apache.org/r/15778
Added build instructions for Mac OS X Mavericks.

From: Niklas Nielsen <nik@qni.dk>
Review: https://reviews.apache.org/r/15727
Fixed master to ignore messages from unregistered framework.

Review: https://reviews.apache.org/r/15773
Reduced the minimum number of cpus per offer to 0.1.

Review: https://reviews.apache.org/r/15774