make history_n integer variables

[jedwards4b]

Description of changes

Change the definition for history_n type variables to integer.

Specific notes

Contributors other than yourself, if any:

CMEPS Issues Fixed (include github issue #):

Are changes expected to change answers? (specify if bfb, different at roundoff, more substantial)

Any User Interface Changes (namelist or namelist defaults changes)?

Testing performed

Please describe the tests along with the target model and machine(s)
If possible, please also added hashes that were used in the testing

[jedwards4b]

@kdraeder can you merge this to your branch and try your tests again? Thanks

[kdraeder]

These fixes seem to work as intended.
The rof2med file was created at the end of the 6 hour forecast, and has time "hour 3.0" in it.
The atm2med settings asked for output every hour, and that's what was created,
with times on the 1/2 hour marks.

A second test had X_history_n = 3 and X_ntperfile = 2
and it put 2 times in each file, at times 1.5 and 4.5, as expected.

So this all seems to be working as I would hope.
I don't have enough context to say whether X_history_option = nhours should be the only choice,
but it does what I need it to.

Thanks!