Enable running SHiELD with a Gregorian calendar

[spencerkclark]

This PR fixes #103 by adding 'GREGORIAN' as an option in the select case statement for inferring the calendar_type in SHiELD's coupler_main.F90. I tested this in a short simulation (including a restart) and things ran without a problem, so this indeed appears as simple as @bensonr suggested.

cc: @lharris4

[bensonr]

@spencerkclark - if you want to use an existing restart, you will need to modify coupler.res (ascii file in INPUT/) and might need to change the value of coupler_nml::calendar. There is a hierarchy of what takes precedence and I believe coupler.res wins all battles.

[spencerkclark]

Thanks @bensonr and @lharris4!

if you want to use an existing restart, you will need to modify coupler.res (ascii file in INPUT/) and might need to change the value of coupler_nml::calendar. There is a hierarchy of what takes precedence and I believe coupler.res wins all battles.

Indeed it makes sense we can still hack that if needed.

[thomas-robinson]

@rem1776 @Scitech777 Is there a current alpha tag for the coupler? Was the coupler tagged with the latest alpha testing tag?

[rem1776]

@thomas-robinson Yeah it was tagged already, I can bump it up to this commit if we want this included.