readrequires: provide easier to understand error message

readrequires: provide easier to understand error message

NEW:

  $ hg id
  abort: unknown repository format: requires feature 'foo' (upgrade Mercurial)!

OLD:

  $ hg id
  abort: requirement 'foo' not supported!

--- a/mercurial/scmutil.py	Tue May 31 19:16:18 2011 +0200
+++ b/mercurial/scmutil.py	Tue May 31 19:16:25 2011 +0200
@@ -698,6 +698,6 @@
     requirements = set(opener.read("requires").splitlines())
     for r in requirements:
         if r not in supported:
-            raise error.RequirementError(
-                _("requirement '%s' not supported") % r)
+            raise error.RequirementError(_("unknown repository format: "
+                "requires feature '%s' (upgrade Mercurial)") % r)
     return requirements

--- a/tests/test-commit.t	Tue May 31 19:16:18 2011 +0200
+++ b/tests/test-commit.t	Tue May 31 19:16:25 2011 +0200
@@ -98,7 +98,7 @@
   $ echo foo >> foo
   $ echo fake >> .hg/requires
   $ hg commit -m bla
-  abort: requirement 'fake' not supported!
+  abort: unknown repository format: requires feature 'fake' (upgrade Mercurial)!
   [255]
 
   $ cd ..

--- a/tests/test-identify.t	Tue May 31 19:16:18 2011 +0200
+++ b/tests/test-identify.t	Tue May 31 19:16:25 2011 +0200
@@ -107,11 +107,11 @@
 
   $ echo fake >> .hg/requires
   $ hg id
-  abort: requirement 'fake' not supported!
+  abort: unknown repository format: requires feature 'fake' (upgrade Mercurial)!
   [255]
 
   $ cd ..
   $ hg id test
-  abort: requirement 'fake' not supported!
+  abort: unknown repository format: requires feature 'fake' (upgrade Mercurial)!
   [255]
 

--- a/tests/test-requires.t	Tue May 31 19:16:18 2011 +0200
+++ b/tests/test-requires.t	Tue May 31 19:16:25 2011 +0200
@@ -9,5 +9,5 @@
   [255]
   $ echo indoor-pool > .hg/requires
   $ hg tip
-  abort: requirement 'indoor-pool' not supported!
+  abort: unknown repository format: requires feature 'indoor-pool' (upgrade Mercurial)!
   [255]