requirements: show all missing features in the error message.

Displaying all missing featureis help people to solve the issue (choosing the
right version, creation the right repo)

mercurial/scmutil.py

@@ -698,10 +698,14 b' def readrequires(opener, supported):'
     '''Reads and parses .hg/requires and checks if all entries found
     are in the list of supported features.'''
     requirements = set(opener.read("requires").splitlines())
+    missings = []
     for r in requirements:
         if r not in supported:
             if not r or not r[0].isalnum():
                 raise error.RequirementError(_(".hg/requires file is corrupt"))
-            raise error.RequirementError(_("unknown repository format: "
-                "requires feature '%s' (upgrade Mercurial)") % r)
+            missings.append(r)
+    missings.sort()
+    if missings:
+        raise error.RequirementError(_("unknown repository format: "
+            "requires features '%s' (upgrade Mercurial)") % "', '".join(missings))
     return requirements

tests/test-commit.t

@@ -98,7 +98,7 b' Make sure we do not obscure unknown requ'
   $ echo foo >> foo
   $ echo fake >> .hg/requires
   $ hg commit -m bla
-  abort: unknown repository format: requires feature 'fake' (upgrade Mercurial)!
+  abort: unknown repository format: requires features 'fake' (upgrade Mercurial)!
   [255]
 
   $ cd ..

tests/test-identify.t

@@ -107,11 +107,11 b' Make sure we do not obscure unknown requ'
 
   $ echo fake >> .hg/requires
   $ hg id
-  abort: unknown repository format: requires feature 'fake' (upgrade Mercurial)!
+  abort: unknown repository format: requires features 'fake' (upgrade Mercurial)!
   [255]
 
   $ cd ..
   $ hg id test
-  abort: unknown repository format: requires feature 'fake' (upgrade Mercurial)!
+  abort: unknown repository format: requires features 'fake' (upgrade Mercurial)!
   [255]
 

tests/test-requires.t

@@ -9,5 +9,9 b''
   [255]
   $ echo indoor-pool > .hg/requires
   $ hg tip
-  abort: unknown repository format: requires feature 'indoor-pool' (upgrade Mercurial)!
+  abort: unknown repository format: requires features 'indoor-pool' (upgrade Mercurial)!
   [255]
+  $ echo outdoor-pool >> .hg/requires
+  $ hg tip
+  abort: unknown repository format: requires features 'indoor-pool', 'outdoor-pool' (upgrade Mercurial)!
+  [255]