Important: Corrected typo in prsgrd42.h and prsgrd44.h

[arango]

• The pressure gradient routines prsgrd42.h and prsgrd44.h use the local variable dP, which is a conflict with the mod_kinds real_kind parameter dp used for double-precision for some selected variables when the solution is mostly in single precision.

Many thanks to Catherine Drinkorn for ​bringing this issue to my attention.

• Adjuted the initialization of the makefile macro libraries to take care of cyclic dependency. It fails in some computer operating system. Now, we have:

    libraries := $(SCRATCH_DIR)/libNLM.a $(SCRATCH_DIR)/libUTIL.a
  

Notice that we add first the dependency for libNLM.a. Many thanks to Bronwyn Cahill for reporting this problem and David Robertson for fixing it.