kes Implement DB Driver = string for the DBI driver.

kes  Remove all old bdb_xxx.c code.  Add dummy routines to bdb.c
kes  First cut of code for loading Win32 plugin dlls. Implement
     dlopen, dlsym, dlclose, and dlerror in src/win32/compat/compat.cpp
     and implement a dlfcn.h file based on opengroup's definitions of
     the functions.