#12 Make seeking work

[John Lindgren]

This patch fixes 3 bugs that were preventing seeks from working correctly:
1. mmsh_seek() was sending the wrong byte offset to the MMS server.
2. mmsh_t::chunk_seq_number was not reset when reaching EOF.
2. mmsh_t::asf_num_packets was never initialized.

[Tom B]

This should be fixed in 0.6.3. Thanks for your patch!