- rrd_open() calculates file size for new files and calls mmap once for

the whole file

- rrd_resize() cleaned up, no longer passing a size through the cookie
argument

- rrd_init(&my_rrd) must be called before rrd_open() - if people are
calling rrd_open directly from application code, this might be
troublesome.  Alternative solutions: creating an additional function,
rrd_open_create(), or adding an extra argument to rrd_open() for setting
the file size

-- Daniel Pocock

git-svn-id: svn://svn.oetiker.ch/rrdtool/trunk/program@1613 a5681a0c-68f1-0310-ab6d-d61299d08faa