lots of bug fixes

• remove dependency on ctypes
• support named pipes on Win32
• report Win32 errors
• client: don't clunk the fid after remove
• client: deallocate_fid should clunk before markind fid as free
• client: remove: always mark the fid as free
• client: don't clunk a fid if walk fails
• server: fix deadlock on Eof which prevents connection cleanup
• use the channel module for buffered packet reading
• unix: don't allocate per request, use a per-connection 32KiB buffer