[Fix] Check for Runtime in DYLD_FALLBACK... on Mac (fixes #32)

Author: johmedr

spm/_spm/__init__.py

@@ -117,8 +117,14 @@ def get_paths_from_os(self):
             raise RuntimeError('Operating system {0} is not supported.'.format(self.system))
 
         path_elements = []
+        
         if self.path_var in os.environ:
             path_elements = os.environ[self.path_var].split(os.pathsep)
+        
+        # On the Mac, do an additional check on DYLD_FALLBACK_LIBRARY_PATH environment variable
+        if not path_elements and self.system == 'Darwin':
+            path_elements = os.environ['DYLD_FALLBACK_LIBRARY_PATH'].split(os.pathsep)
+
         if not path_elements:
             if self.system == 'Darwin':
                 raise RuntimeError('On the Mac, you must run mwpython rather than python ' +