WIP: Makefile switch from wget to curl for downloads.

Currently, quicklisp is downloaded by wget. Curl is a suitable alternative, which can be enhanced with additional params in this case to ensure an updated copy is downloaded. Explanation of parameters below.

-s: silent, no progress bar displayed -S: if silent, shows error message on fail -L: in case of redirection, follow it and redo the request; this is necessary to correctly get modification date -f: in case of error do not display the document returned -z my_local_file: download remote file only if last modification date more recent that modification date of 'my_local_file' -o filename: store downloaded file into 'filename'