alias: shortcut command matching show shadowing works properly (issue3104)

An alias for 'log' was stored in the same command table as
'^log|history'. If the hash function happens to give the latter first,
the alias is effectively ignored when matching 'log'.

mercurial/cmdutil.py

@@ -23,7 +23,14 b' def findpossible(cmd, table, strict=Fals'
     """
     choice = {}
     debugchoice = {}
-    for e in table.keys():
+
+    if cmd in table:
+        # short-circuit exact matches, "log" alias beats "^log|history"
+        keys = [cmd]
+    else:
+        keys = table.keys()
+
+    for e in keys:
         aliases = parsealiases(e)
         found = None
         if cmd in aliases:

tests/test-alias.t

@@ -395,3 +395,11 b' invalid global arguments for normal comm'
   use "hg help" for the full list of commands or "hg -v" for details
   [255]
 
+This should show id:
+
+  $ hg --config alias.log='id' log
+  000000000000 tip
+
+This shouldn't:
+
+  $ hg --config alias.log='id' history