Add support for MySQL 5.5/5.6

The mysql plugin named "mysql_" have a problem. So It could not work
fine with MySQL 5.5 or 5.6.
I have make a patch for "INDIVIDUAL BUFFER POOL INFO" section as
skipped to work.

## all of symlinked mysql_ pluugin gets error like below.
```sh
$ /etc/munin/plugins/mysql_connections
Unknown section: INDIVIDUAL BUFFER POOL INFO at
/etc/munin/plugins/mysql_connections line 1098.
```

## related issue
https://github.com/kjellm/munin-mysql/commit/111293966ccd6e8df6c1347cb0f
9a8b4025c0266
mysql_innodb_insert_buf compatibility problem fixed for MySQL 5.5/5.6

The mysql plugin named "mysql_" have a problem. So It could not work
fine with MySQL 5.5 or 5.6.
I have make a patch for "mysql_innodb_insert_buf" to work.

## symlinked from mysql_innodb_insert_buf to mysql_ pluugin gets error
below.
```sh
$ /etc/munin/plugins/mysql_innodb_insert_buf
Use of uninitialized value in printf at
/etc/munin/plugins/mysql_innodb_insert_buf line 885.
ib_ibuf_inserts.value
Use of uninitialized value in printf at
/etc/munin/plugins/mysql_innodb_insert_buf line 885.
ib_ibuf_merged_rec.value
Use of uninitialized value in printf at
/etc/munin/plugins/mysql_innodb_insert_buf line 885.
ib_ibuf_merges.value
```

## related issue
https://github.com/kjellm/munin-mysql/issues/34#issuecomment-1487824
fixed indent
add verified version for mysql_ plugin
Merge pull request #109 from y-ken/support_mysql55_later

fixed compatibility issue for "mysql_" plugin with MySQL 5.5/5.6.