issue #65: fix some shell escaping for building in a dir with spaces

When I manually patch my "NODE_PREFIX/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js" with this patch, then at least https://github.com/chrisa/node-dtrace-provider/issues/25 (and hence https://github.com/trentm/node-bunyan/issues/58) is fixed.