Don't let deletions leak from OverrideEnvironment

Previously, deleting from an OverrideEnvironment removed not just the
override item but also the same item in the subject (base) environment.
This prevents supplying the value from the subject, as that would be
contrary to the expectation after "I deleted this variable".  However,
this lets the override modify its subject, a form of leakage we don't
want. Now a deleted item has its key recorded to prevent refilling
later. Direct assignment will still set the item back in the override.

rpm packaging tool: call Override factory method rather than directly
instantiating OverrideEnvironment ("best practices")

Signed-off-by: Mats Wichmann <[email protected]>

CHANGES.txt

@@ -12,9 +12,16 @@ NOTE: Python 3.6 support is deprecated and will be dropped in a future release.
 
 RELEASE  VERSION/DATE TO BE FILLED IN LATER
 
-      From John Doe:
-
-        - Whatever John Doe did.
+  From Mats Wichmann:
+    - Override envirionments, created when giving construction environment
+      keyword arguments to Builder calls (or manually, through the undocumented
+      Override method), were modified not to "leak" on item deletion.  The item
+      will now not be deleted from the base environment.  Methods of regular
+      environments modified to (mostly) not directly access the _dict attribute
+      which stores the construction variables - in case they're called via
+      proxying from an OverrideEnv, which does not have such an attribute
+      (though for completeness, it now pretends to).  Let the dictionary-like
+      methods handle access/update instead.
 
 
 RELEASE 4.8.1 -  Tue, 03 Sep 2024 17:22:20 -0700

RELEASE.txt

@@ -29,6 +29,11 @@ CHANGED/ENHANCED EXISTING FUNCTIONALITY
 - List modifications to existing features, where the previous behavior
   wouldn't actually be considered a bug
 
+- Override envirionments, created when giving construction environment
+  keyword arguments to Builder calls (or manually, through the
+  undocumented Override method), were modified not to "leak" on item deletion.
+  The item will now not be deleted from the base environment.
+
 FIXES
 -----