check-code: make repquote distinguish more characters for exact detection
This patch makes repquote() distinguish more characters below, as a
preparation for exact detection in subsequent patch.
- "%" as "%"
- "\\" as "b"(ackslash)
- "*" as "A"(sterisk)
- "+" as "P"(lus)
- "-" as "M"(inus)
Characters other than "%" don't use itself as replacement, because
they are treated as special ones in regexp.
check-code: centralize rules depending on implementation of repquote
This decreases the cost of checking which regexp should be adjusted at
change of repquote().