remove an allocatable pointer in transportmod

Now an allocatable pointer is replaced with a target type.
All tests passed with OSX gnu 8 compilers.

Merge pull request BeTR-biogeochemistry-modeling#23 from BeTR-biogeoc…

…hemistry-modeling/bishtgautam/rename-shr-nl-mod

Renames shr_nl_mod to bshr_nl_mod