ui: disable revsetaliases in plain mode (BC)

ui.plain() is supposed to disable config options that change the UI to the
detriment of scripts. As the test demonstrates, revset aliases can actually
override builtin ones, just like command aliases. Therefore I believe this is a
bugfix and appropriate for stable.

mercurial/ui.py

@@ -169,6 +169,9 b' class ui(object):'
         if self.plain('alias'):
             for k, v in cfg.items('alias'):
                 del cfg['alias'][k]
+        if self.plain('revsetalias'):
+            for k, v in cfg.items('revsetalias'):
+                del cfg['revsetalias'][k]
 
         if trusted:
             self._tcfg.update(cfg)

tests/test-revset.t

@@ -1049,6 +1049,8 b' aliases:'
 
   $ echo '[revsetalias]' >> .hg/hgrc
   $ echo 'm = merge()' >> .hg/hgrc
+(revset aliases can override builtin revsets)
+  $ echo 'p2($1) = p1($1)' >> .hg/hgrc
   $ echo 'sincem = descendants(m)' >> .hg/hgrc
   $ echo 'd($1) = reverse(sort($1, date))' >> .hg/hgrc
   $ echo 'rs(ARG1, ARG2) = reverse(sort(ARG1, ARG2))' >> .hg/hgrc
@@ -1064,6 +1066,58 b' aliases:'
     <fullreposet+ 0:9>>
   6
 
+  $ HGPLAIN=1 try m
+  ('symbol', 'm')
+  abort: unknown revision 'm'!
+  [255]
+
+  $ HGPLAIN=1 HGPLAINEXCEPT=revsetalias try m
+  ('symbol', 'm')
+  (func
+    ('symbol', 'merge')
+    None)
+  * set:
+  <filteredset
+    <fullreposet+ 0:9>>
+  6
+
+(for some reason HGPLAIN and HGPLAINEXCEPT can carry forward)
+
+  $ unset HGPLAIN
+  $ unset HGPLAINEXCEPT
+
+  $ try 'p2(.)'
+  (func
+    ('symbol', 'p2')
+    ('symbol', '.'))
+  (func
+    ('symbol', 'p1')
+    ('symbol', '.'))
+  * set:
+  <baseset+ [8]>
+  8
+
+  $ HGPLAIN=1 try 'p2(.)'
+  (func
+    ('symbol', 'p2')
+    ('symbol', '.'))
+  * set:
+  <baseset+ []>
+
+  $ HGPLAIN=1 HGPLAINEXCEPT=revsetalias try 'p2(.)'
+  (func
+    ('symbol', 'p2')
+    ('symbol', '.'))
+  (func
+    ('symbol', 'p1')
+    ('symbol', '.'))
+  * set:
+  <baseset+ [8]>
+  8
+
+  $ unset HGPLAIN
+  $ unset HGPLAINEXCEPT
+
 test alias recursion
 
   $ try sincem