fix ansi filter regex for GNU sed #123

Different seds interpret ? and \? differently, both can be a
metacharacter. As in the case of FreeBSD sed and GNU sed respectively.

Use [?] for a literal ?, this is safe on all seds.

vimpager

@@ -707,7 +707,7 @@ find_rc() {
 }
 
 ansi_filter() {
-	sed -e 's/\[;*\?*\([0-9.]*\(;[0-9]*\)*\)*[A-Za-z]//g'
+	sed -e 's/\[;*[?]*\([0-9.]*\(;[0-9]*\)*\)*[A-Za-z]//g'
 }
 
 # Normally, filter outputs overstrike free content to STDERR.