USE_WINDOWS_SSPI on Windows, and then libcurl will be built to use the native
way to do NTLM. SSPI also allows libcurl to pass on the current user and its
password in the request.

Renamed import lib to "libcurl_imp.lib".
Some cleanup and making it more readable.

Changes for removing libcurl.def file on Win32.
Added "CURL_EXTERN" to memdebug.h functions.
Cleaned up Makefile.vc6.

might be done differently in the future.

machines.