Revision 56

Imported "writehist.f" from LMDZ.

Moved module variable "histaveid" from "com_io_dyn" to "initdynav_m".

In "inithist", access directly module variables from "com_io_dyn"
instead of going through the arguments. Copying from LMDZ, write "u"
and scalar variables to separate files. Create a new variable for the
new file in "com_io_dyn". Copying from LMDZ, change the vertical axes
of the three files.

Removed some useless initializations in "dissip".

In "bilan_dyn", removed useless variable "time". Avoiding the
approximate test on "dt_cum" being a multiple of "dt_app", just
compute "ncum" from known usage of "bilan_dyn" and compute "dt_cum"
from "ncum". Change "periodav" from real to integer in
"conf_gcm_m". Since "day_step" is required to be a multiple of
"iperiod", so is "ncum".