[cmyth] Win32: Add cmyth_msc.h to project files
[cmyth] Win32: Fix socket connection hang

Functions in libcmyth usually return a negative error value (-ERRNO).
An incorrect define made functions that return the error -ECANCELED
and -ETIMEDOUT a positive value, indicating a successful operation.
Due to this, socket connection problems were not handled correctly
on Windows.

Affected functions are cmyth_conn_check_block, cmyth_file_read,
cmyth_ringbuf_read, cmyth_send_message, cmyth_rcv_length,
cmyth_conn_refill and cmyth_rcv_data.

One manifestation is that a restart of the backend caused the addon
to hang.
[cmyth] Removed commented out lines from cmyth_msc.h