hooks: forbid ':' in hook name stable

hooks: forbid ':' in hook name

The `:` character is a special separator in the config and it seems same do to
the same for hooks. This is necessary to improve the experience around the
HGPLAIN behavior change in 5.7. See next changesets for details.

Differential Revision: https://phab.mercurial-scm.org/D9978

--- a/mercurial/configitems.py	Wed Feb 10 21:46:29 2021 +0100
+++ b/mercurial/configitems.py	Wed Feb 10 21:05:05 2021 +0100
@@ -1310,7 +1310,7 @@
 )
 coreconfigitem(
     b'hooks',
-    b'.*',
+    b'[^:]*',
     default=dynamicdefault,
     generic=True,
 )

--- a/mercurial/hook.py	Wed Feb 10 21:46:29 2021 +0100
+++ b/mercurial/hook.py	Wed Feb 10 21:05:05 2021 +0100
@@ -224,7 +224,11 @@
     """return all hooks items ready to be sorted"""
     hooks = {}
     for name, cmd in ui.configitems(b'hooks', untrusted=_untrusted):
-        if name.startswith(b'priority.') or name.startswith(b'tonative.'):
+        if (
+            name.startswith(b'priority.')
+            or name.startswith(b'tonative.')
+            or b':' in name
+        ):
             continue
 
         priority = ui.configint(b'hooks', b'priority.%s' % name, 0)