The counter handler_read_key (SSV::ha_read_key_count) is incremented 
incorrectly.

The mysql server maintains a per thread system_status_var (SSV)
object.  This object contains among other things the counter
SSV::ha_read_key_count. The purpose of this counter is to measure the
number of requests to read a row based on a key (or the number of
index lookups).

This counter was wrongly incremented in the
ha_innobase::innobase_get_index(). The fix removes
this increment statement (for both innodb and innodb_plugin).

The various callers of the innobase_get_index() was checked to
determine if anybody must increment this counter (if they first call
innobase_get_index() and then perform an index lookup).  It was found
that no caller of innobase_get_index() needs to worry about the
SSV::ha_read_key_count counter.