Fix a bit of slight sloppiness in variable usage.

The "'atlas' in libs" line should really be "'atlas' in libraries"
This was still working due to Python's loop variable leakage, but
from the logic it's clear that the `libraries` variable was intended
to be used here.

build/pkgs/atlas/spkg-install

@@ -143,6 +143,7 @@ if 'SAGE_ATLAS_LIB' in os.environ:
 
     paths = [ ATLAS_LIB, os.path.join(ATLAS_LIB, 'lib64'), os.path.join(ATLAS_LIB, 'lib') ]
     ATLAS_LIB = None
+    libraries = []
     for libs in libraries_sets:
         for path in paths:
             if is_atlas_lib_path(path, libs):
@@ -209,7 +210,7 @@ if 'SAGE_ATLAS_LIB' in os.environ:
     for lib in libraries + libraries_optional:
         symlinkOSlibrary(prefix+lib)
 
-    if 'atlas' in libs:
+    if 'atlas' in libraries:
         write_pc_file(['cblas', 'atlas'], 'cblas')
         write_pc_file(['f77blas', 'atlas'], 'blas')
         # The inclusion of cblas is not a mistake. ATLAS' lapack include