- Adding more robust code to handle the case where the exec call within spawn fails. Now, spawn will raise an exception if this happens.
 - Adding a test to ensure this exception is raised when an invalid binary is run
 - Addressing all of the points raised by @takluyver in
   https://github.com/pexpect/ptyprocess/pull/1 with the
   exception of the generic exec OSError handling - waiting
   on thoughts on how best to implement this.
 - In the case where exec fails, the errno returned in the exception is now the one returned from the child process exception
 - Minor improvements to the exec failure test case
 - Simplifying some of the exec failure test code based on suggestions from @takluyver
Merge pull request #1 from anwilli5/master

Potential fix for 'exec' failure case