Changes to support a more robust command interface.  Again, a big thanks
to @hb--.  These changes are based hugely on his patch submitted under
issue #5.  With a few minor changes these are included in vmsshell.c.  I
still have some simple testing to do, to make sure it still hangs together
after my mangling.
First dumb typo...
Change SQLITERC to SQLITE_INIT on OpenVMS.
Couple minor corrections to formatting.
Correction to file open mode (so we don't end up with trillions of versions
of the history file).  Also, replaced call to rewind with ftruncate.
Final changes to vmsshell.  Truncating properly, fixed open mode.