Updated changelog to highlight backward-incompatible changes

CHANGES.txt

@@ -13,13 +13,6 @@ CHANGES
   the ``SETUPTOOLS_USE_PYLAUNCHER`` environment variable is set (to anything).
   In the future, this behavior may become default, but only after it has
   matured and seen substantial adoption.
-* Issue #50: Normalized API of environment marker support. Specifically,
-  removed line number and filename from SyntaxErrors when returned from
-  `pkg_resources.invalid_marker`. Any clients depending on the specific
-  string representation of exceptions returned by that function may need to
-  be updated to account for this change.
-* Issue #50: SyntaxErrors generated by `pkg_resources.invalid_marker` are
-  normalized for cross-implementation consistency.
 * Issue #63: Bootstrap script (ez_setup.py) now prefers Powershell, curl, or
   wget for retrieving the Setuptools tarball for improved security of the
   install. The script will still fall back to a simple ``urlopen`` on
@@ -28,6 +21,16 @@ CHANGES
 * Issue #52: In ``VerifyingHTTPSConn``, handle a tunnelled (proxied)
   connection.
 
+Backward-incompatible changes:
+
+* Issue #50: Normalized API of environment marker support. Specifically,
+  removed line number and filename from SyntaxErrors when returned from
+  `pkg_resources.invalid_marker`. Any clients depending on the specific
+  string representation of exceptions returned by that function may need to
+  be updated to account for this change.
+* Issue #50: SyntaxErrors generated by `pkg_resources.invalid_marker` are
+  normalized for cross-implementation consistency.
+
 -----
 0.9.8
 -----