buffering history text file writes

[Ilya Etingof]

> How match time take "history write" with and without this hack --
> several minutes per day ? :)

Before the hack:

Code region    Time           Pct   Invoked   Min(ms)  Avg(ms)   Max(ms)
history write  02:38:09.441   11.4% 1192178   0.049    7.960     143.136

After hack:

Code region    Time           Pct   Invoked   Min(ms)  Avg(ms)   Max(ms)
history write  00:46:48.733   3.3%  1443047   0.047    1.946     161.819

Although the above stats is not particularily accurate (I was changing
other things to the machine at the same time I was playing with the hack),
I guess it's still more or less representative.

Note, however, that the disk where my history lives is somewhat slow (you
see the figures) so the saving resulted by this hack might not be really
noticable if your history disks are so fast that your system spends just
a few minutes a day on history writes.

-ilya