fix two bugs in sed code configure uses to save command line

one place where semicolon (non-portable) was still used in place of
separate -e options (copied over from an old version of this code),
and use of a literal slash in the bracket expression for the final
command, despite slash being used as the delimiter for the s command.

configure

@@ -49,7 +49,7 @@ quote () {
 tr '\n' ' ' <<EOF | grep '^[-[:alnum:]_=,./:]* $' >/dev/null 2>&1 && { echo "$1" ; return 0 ; }
 $1
 EOF
-printf %s\\n "$1" | sed -e "s/'/'\\\\''/g" -e "1s/^/'/;\$s/\$/'/" -e "s/^'\([-[:alnum:]_,./:]*\)=\(.*\)\$/\1='\2/"
+printf %s\\n "$1" | sed -e "s/'/'\\\\''/g" -e "1s/^/'/" -e "\$s/\$/'/" -e "s#^'\([-[:alnum:]_,./:]*\)=\(.*\)\$#\1='\2#"
 }
 echo () { printf "%s\n" "$*" ; }
 fail () { echo "$*" ; exit 1 ; }