Correct “an” → “a” with “Unicode”, “user”, “UTF”, etc

This affects documentation and code comments.
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index c6e3d39..cf6402f 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -574,7 +574,7 @@
 # @param text A string containing the QName value, in the form {uri}local,
 #     or, if the tag argument is given, the URI part of a QName.
 # @param tag Optional tag.  If given, the first argument is interpreted as
-#     an URI, and this argument is interpreted as a local name.
+#     a URI, and this argument is interpreted as a local name.
 # @return An opaque object, representing the QName.
 
 class QName(object):