mysys: THR_LOCK_open reduce usage

Change the following to statistic counters:

my_file_opened

my_file_total_opened

my_stream_opened

my_tmp_file_created

There is one non-statistics use of my_file_opened/my_stream_opened

in my_end which prints a warning if we shutdown and its still open.

It seems excessive to hold locks to prevent this warning.

A file descriptor is already a unique element - in Windows protection

occurs at fd allocation using THR_LOCK_open in my_win_fopen

and in other OSes, a unique fd to file map exists at the OS level.

So accesses to my_file_info[fd] don't need to be protected by the

THR_LOCK_open.

my_close/my_fclose where restructured to clear out the my_file_info

before the close/my_win_close. After these calls another thread could

gain the same file descriptor. Windows doesn't need THD_LOCK_open

into my_win_close as there is no conflict with the my_win_fopen in allocating a fd.

my_fclose also changed for non-Windows to retry closing if EINTR was

returned, same as my_close..

FYI @vaintroub

Pathological cases - two threads attempt to close the same file at same time at which there is a chance of double free. If there is this case, there's a equal failing that the file descriptor could have been reallocated before the second close call was complete, also leading to wrongness.