A better fix for the WIN32_VSS bug that Kern discovered.

Create a separate DLL for each database interface.  Then rename it to
bacula_cats.dll during installation.

Move sql_cmd.c from src/dird to src/cats.

Create a header file for the constants exported from sql_cmd.c.

Removed local extern definitions from cats *.c files, put them in sql_cmd.h.

Added Windows version of the database scripts.  In some cases these scripts are placeholders and more work is needed to make them execute.

Eliminated the need to install the database dlls in a client only installation.