Revert "This commit adds nsh_consolechild().  I noticed that there are several examples that call nsh_consolemain.c to create to create a new NSH session.  That will not always work because nsh_consolemain() performs the one-time initialization needed by the NSH library:  Mounting, reading, and running the start-up script, configuring USB tracing.  Some of those actions will cause failures if attempted twice."

This reverts commit 4d364d83.

This commit adds nsh_consolechild().  I noticed that there are several examples that call nsh_consolemain.c to create to create a new NSH session.  That will not always work because nsh_consolemain() performs the one-time initialization needed by the NSH library:  Mounting, reading, and running the start-up script, configuring USB tracing.  Some of those actions will cause failures if attempted twice.

Here are some offenders: examples/cc3000/shell.c, examples/nsh/nsh_main.c, examples/nxterm/nxterm_main.c, and examples/pty_test/pty_test.c.  It is possible that for some of those, that represents the first call to nsh_consolemain().  But probably not.

To give other initialization options, I added nsh_consolechild() which is identical to nsh_consolemain() other than it omits all of the one-time initialization.  Of course, you would not get the result that you wanted if nsh_consolechild() were called without nsh_consolemain().

apps/examples/system:  Add a simple test of the system command.  Fix the first bug discovered by the test.

apps/system/system:  Add a generic system command.  Current implentation cannot use /bin/sh and spawns the custom NSH system command directly.

apps/nshlib/nsh_syscmds.c: missing semicolon

apps/examples/oneshot:  If the requested delay is > max_delay, then break the delay up into several pieces.

apps/interpreters/minibasic:  Add a port of Mini Basic, version 1.0, written by Malcom McLean and released under the Creative Commons Attirbution license.