Check species constraints in consistent order.

Doesn't make a real difference, just easier for a human 
to parse the code without making errors, when the "if" 
blocks are in the same order as the documentation and examples.

Author: rwest

rmgpy/constraints.py

@@ -108,6 +108,11 @@ def fails_species_constraints(species):
         if struct.get_num_atoms('S') > max_sulfur_atoms:
             return True
 
+    max_heavy_atoms = species_constraints.get('maximumHeavyAtoms', -1)
+    if max_heavy_atoms != -1:
+        if struct.get_num_atoms() - struct.get_num_atoms('H') > max_heavy_atoms:
+            return True
+
     max_surface_sites = species_constraints.get('maximumSurfaceSites', -1)
     if max_surface_sites != -1:
         if struct.get_num_atoms('X') > max_surface_sites:
@@ -119,11 +124,6 @@ def fails_species_constraints(species):
             if site.get_total_bond_order() > max_surface_bond_order:
                 return True
 
-    max_heavy_atoms = species_constraints.get('maximumHeavyAtoms', -1)
-    if max_heavy_atoms != -1:
-        if struct.get_num_atoms() - struct.get_num_atoms('H') > max_heavy_atoms:
-            return True
-
     max_radicals = species_constraints.get('maximumRadicalElectrons', -1)
     if max_radicals != -1:
         if struct.get_radical_count() > max_radicals: