article 'a' for Angel names

The recently revised priestname(), which is also used for angels
since they share the " of <deity>" suffix, included a test for
'!strncmp(,"Angel ",6)', assuming it was looking at the beginning
of "Angel of <deity>".  But the " of <deity>" part doesn't get
appended until later, so the test should be '!strcmp(,"Angel")'
without the trailing space.

Noticed by code inspection; I don't have a test case.  Like priests,
Angels are almost always referred to as "_the_ Angel of <deity>" so
the bad "Angel " check normally wouldn't get reached.

Also, fix an unrelated indentation bit in fixes3-7-0.txt.

doc/fixes3-7-0.txt

@@ -119,7 +119,7 @@ tribute (Discworld snippets) typos, in book order rather than fix order:
 	 #12 "or" -> "of", #14 second instance of "megalomaniac" misspelled
 	Lords and Ladies passage #5, near end add missing opening double
 	 quote, passage #6 first footnote, insert omitted "be", passage #7
-	last paragraph, "to" -> "be"
+	 last paragraph, "to" -> "be"
 	Men at Arms passage #1, italicize /for/, passage #2, insert omitted
 	 word "had": 'it was /fate/ that _had_ let Edward'
 	Interesting Times passage #1, italicize several words