updated makefile's clean routine to remove all ignored files
updated makefile's clean routine to remove all ignored files

This might be dangerous, but since we're (currently?) using .gitignore
only for third-party libraries, it's rather convenient.

TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,FND/tiddlyspace,FND/tiddlyspace,FND/tiddlyspace