Temporary (or anonymous) function handles for ML 6

Creates a temporary function m-file and returns a handle to it.

The anonymous function handle feature of ML 7 is a long-needed feature, and one that I have longed for since I began writing scripts in early ML 6.

Unfortunately, I am still forced to use ML 6 most of the time, so I came up with a way to create "psuedo-anonymous" function handles: that is, function handles to real m-file functions that are created on the spot and will be deleted in the near future.

TMP_HANDLE writes out a temporary function m-file in its private subdirectory and then returns a handle to it. As a side effect, it searches for old temporary function files and deletes them.

I have TMP_HANDLE set to delete temporary function m-files that are older than 30 days. The whole idea of cluttering up a subdirectory with little m-files is distasteful, but not really a big deal given modern disk sizes. I have chosen to live with it.

Next step:
Make TMP_HANDLE a class with overloaded feval and subsref so you can call
feval(t_hndl,x,y)
OR just
t_hndl(x,y)

Matlab 5 has feval and classes with overloading, so making tmp_handle a class should allow it to work with ML 5.