Read 16-bit McIdas images into I;16B mode to allow for memory mapping

[radarhere]

Pillow/src/PIL/McIdasImagePlugin.py

Lines 53 to 55 in a370209

	# FIXME: add memory map support
	mode = "I"
	rawmode = "I;16B"

This FIXME can be resolved by changing the mode to match the rawmode.

Pillow/src/PIL/Image.py

Lines 276 to 278 in a370209

	# raw modes that may be memory mapped. NOTE: if you change this, you
	# may have to modify the stride calculation in map.c too!
	_MAPMODES = ("L", "P", "RGBX", "RGBA", "CMYK", "I;16", "I;16L", "I;16B")

Pillow/src/PIL/ImageFile.py

Lines 308 to 316 in a370209

	if (
	decoder_name == "raw"
	and isinstance(args, tuple)
	and len(args) >= 3
	and args[0] == self.mode
	and args[0] in Image._MAPMODES
	):
	try:
	# use mmap, if possible