add meta-types for landunit types

**Bill Sacks < sacks@ucar.edu > - 2012-03-22 16:20:18 -0600**
**Bugzilla Id:** [1483](http://bugz.cgd.ucar.edu/show_bug.cgi?id=1483)
**Bugzilla CC:** rfisher@ucar.edu,

There are lots of checks in the code that look like this:

if (ltype(l) == istsoil .or. ltype(l) == istcrop)

or:

if (ltype(l)==istice .or. ltype(l)==istice_mec) then

or:

elseif ( itypelun(l) == istdlak .or. itypelun(l) == istslak ) then

I would propose adding some logical variables like:

is_vegetated(l) (true for soil & crop landunits)

is_ice(l) (true for ice & ice_mec landunits)

is_lake(l) (true for deep & shallow lake)

This would have these advantages:

- more easily extensible: e.g., could add a new vegetated landunit without having to change conditionals that occur throughout the code

- safer: e.g., I just found an instance where a conditional checked ltype(l)==istice, forgetting to also check the possibility of istice_mec