changes to mtr_commit:

1) grab log mutex (and do initial mtr commit stuff)
for each dirty block
 2) grab flush_list mutex
 3) Insert into flush list
 4) release flush_list mutex
5) release log_sys mutex

Changed version:

1) grab log mutex (and do initial mtr commit stuff)
2) grab a new flushList order mutex
3) release log mutex
for each dirty block
 4) grab flush_list mutex
 5) Insert into flush list
 6) release flush_list mutex
7) Release new flush list order mutex 

Approved by: Marko has given the initial nod.