Change the name of the local variable sigset to set to prevent name collisions with the function of the same name

Readline: Fix a configuration dependency.  If we are not echoing to the console, then we cannot support tab completion

readline/NSH: Extend the tab-completion logic so that NSH commands can also be completed by pressing the tab key

readline: Update initial readline commit -- make option configurable.  Add an interface to de-couple the readline implementation from NSH.  Misc. updates for coding style

Unix style TAB compleition, for builtin apps only

OS test: Sporadic test now emits a message if the max_repl configuration is too small for the test to work reliably

OS test: add some locking and unlocking of the scheduler to the sporadic scheduler test in order to test a few more cases

netutils: fix a typo while validating addrlen

Adjust for increased size of the scheduling policy field from 1 to 2 bits to allow additional, planned scheduling policies

NSH: Fix compile issue from all of the recent NETDB changes.  If NETDB is not enabled, we need to use inet_pton() instead of gethostbyname()