Disable netrw until I can fix the broken mappings.

Colemak.vim is probably to blame.
Bring mpvim up to MacPorts r101674.
Remove filetype setting for MacPorts portfiles.

The issue here was that portfiles' modelines set "filetype" to "tcl",
which overrode mpvim's "portfile" filetype.  I fixed mpvim in MacPorts
r101624 so that portfile buffers disable modelines; thus, this
BufWinEnter hack is no longer necessary.
Bring mpvim up to MacPorts r101984.