Up until now the fts4 "unicode61" tokenizer has treated all private use codepoints except the first and last of each of the three ranges as alphanumeric (eligible to be part of tokens). This commit fixes this so that all private use codepoints are considered alphanumeric. In other words, it fixes the handling of codepoints 0xE000, 0xF8FF, 0xF0000, 0xFFFFD, 0x100000 and 0x10FFFD.