errno feature branch

[Gregory Nutt]

FYI..

I have just create a branch called 'errno' in both incubator_nuttx and 
incubator_nuttx_apps.  This is where we will be implementing new errno 
support as documented in Issue #986 "Userspace errno" 
(https://github.com/apache/incubator-nuttx/issues/986)

The implementation is not so complex that it requires a feature branch.  
However, there is some risk in changing the errno implementation so it 
is best that we test all that we can on a feature branch before merging 
to master.

Greg