decode_long(data)
Decode a long from a two's complement little-endian binary string.
>>> decode_long('') 0L >>> decode_long("\xff\x00") 255L >>> decode_long("\xff\x7f") 32767L >>> decode_long("\x00\xff") -256L >>> decode_long("\x00\x80") -32768L >>> decode_long("\x80") -128L >>> decode_long("\x7f") 127L