[Ecls-list] library loading in Windows, again

[Dustin Long]

The last patch for loading libraries, which copied each load target to a 
temporary location first, has introduced some other problems (for 
Windows only). In some cases, when loading the same library multiple 
times, one wants only a single copy to actually be instantiated. For 
example, when using ffi to connect to a foreign library, loading 
multiple copies will cause problems since each library will get their 
own set of instance data, rendering separate ffi:def-functions 
incompatible with each other.

I propose the following solution. When a library is loaded by 
ecl_library_open, check first if the file's modified time is newer than 
the already loaded library's. If so, continue with loading, otherwise 
return the already loaded codeblock. It's not very elegant, but works 
pretty well. Maybe the code should be refactored though, perhaps making 
file-date-comparing a separate function.

Along with the patch, test code is attached (getset.cpp is a dll, 
usage.lisp an ffi client)

Before patching: (progn (set-value 3) (get-value)) => 0
After patching: (progn (set-value 3) (get-value)) => 3

Another thing I noticed was that during ecl_library_open, a codeblock's 
name is assigned the value of the filename loaded, even when that file 
first gets copied to a temp. This doesn't seem right, as what really 
needs to be tracked is the original library path. The attached patch 
also fixes this. There aren't any adverse side effects from this change, 
are there?

Dustin
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