[PATCH STABLE] help: mention alias and revsetalias in description of HGPLAINEXCEPT

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1445666366 -3600
#      Sat Oct 24 06:59:26 2015 +0100
# Branch stable
# Node ID a9ed5a8fc5e0554d5cb81b7206d2203cc49a2d23
# Parent  39dbf495880b8a439d912091109427d27a7e616a
help: mention alias and revsetalias in description of HGPLAINEXCEPT

diff --git a/mercurial/help/environment.txt b/mercurial/help/environment.txt
--- a/mercurial/help/environment.txt
+++ b/mercurial/help/environment.txt
@@ -61,8 +61,14 @@ HGPLAIN
 
 HGPLAINEXCEPT
     This is a comma-separated list of features to preserve when
-    HGPLAIN is enabled. Currently the only value supported is "i18n",
-    which preserves internationalization in plain mode.
+    HGPLAIN is enabled. Currently the following values are supported:
+
+    ``alias``
+        Don't remove aliases.
+    ``i18n``
+        Preserve internationalization.
+    ``revsetalias``
+        Don't remove revset aliases.
 
     Setting HGPLAINEXCEPT to anything (even an empty string) will
     enable plain mode.