Added new primitive: is_maildir.

  This was part of #93, and seemed like a sensible addition.

  Documented:  http://lumail.org/lua/is_maildir.html
  New static member: CMaildir::create()

  This will be used by the new lua primitive "create_maildir",
 or whatever it is called.  Updates #93.
  New primitive: create_maildir().

  This could be used for the save message primitive, etc.

  TODO: Document.

  This updates #93.
  Use the LVER to define the lua version to compile against.
  Remove any core-file on "make clean".
  Don't try to decode header-fields.

  The code in place was bogus, we need a real solution.

  This is part of #66.
  Simplify --folder handling.

  We don't need to evaluate so much these days, now we have
 better primitives.
  Cleanup the stack better.

  This should close #94.
  Updated to remove prototype for orphaned function.
  Comment out sent_folder by default.

  Although we have wrapped it in an "is_maildir" test
 we've removed this by default.

  This closes #93.
  Updated the handling of sent_path.

  Now that we accept it might be NULL we need to care
 a little more about it.
  ENsure we have a mode setup.
  Allow user to disable case-insensitive tab-completion.

  The new variable "ignore_case" can disable/enable tab-completion
 being case insensitive, as per the documentation:

    http://lumail.org/faq/technical/
make build succeed on older g++ version by reordering args
  Only log variable setting when in debug-mode.

  This was probably harmless, but it doesn't hurt to be
 correct.
  Better logging of variable/table fetching.
Add gdb debug symbols in debug build
  Only call the deletion of the file once.

  This updates #95.
  Added logging to lua callbacks.

  This is part of #95.  I'm wondering if the on_idle callback
 is happening at teh same time as the on_message_parse code is
 running.

  Since we borrow the m_lua member from CLua for the duration
 it is possible we're seeing corruption of the internal state
that way.

  Adding a mutex would help narrow that down; but that means
 pthreads..
  Use pointers so we're sure that the lua-value never
 goes out of scope / falls off the stack.

  This updates #95