"and extra" breaks environment marker logic

[jaraco]

In pypa/setuptools#1242, we discovered that wheel is allegedly simply appending and extra=="...", which will break the logic when the existing environment marker contains or expressions.

[benoit-pierre]

Tentative patch:

 wheel/metadata.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git i/wheel/metadata.py w/wheel/metadata.py
index 29638e7..75dce67 100644
--- i/wheel/metadata.py
+++ w/wheel/metadata.py
@@ -255,7 +255,7 @@ def generate_requirements(extras_require):
         if extra:
             yield ('Provides-Extra', extra)
             if condition:
-                condition += " and "
+                condition = "(" + condition + ") and "
             condition += "extra == '%s'" % extra
         if condition:
             condition = '; ' + condition