spark-class.cmd produced null command strings for "exec"

When using the run-example script in 1.4.0 to run the SparkPi example, I found that it did not print any text to the terminal (e.g., stdout, stderr). After further investigation I found the while loop for producing the exec command from the launcher class produced a null command array.

This discrepancy was observed on 1.5.2 and 1.4.1. The 1.3.1's behavior seems to be correct.