bookmarks: abort directly on invalid name

This consolidates the abort message for a bookmark name containing
invalid characters into one place, and renames the valid() method to
checkvalid() to reflect the fact that it's no longer a predicate.

mercurial/bookmarks.py

@@ -10,11 +10,11 b' from mercurial.node import hex'
 from mercurial import encoding, error, util, obsolete, phases
 import errno, os
 
-def valid(mark):
+def checkvalid(mark):
     for c in (':', '\0', '\n', '\r'):
         if c in mark:
-            return False
-    return True
+            raise util.Abort(_("bookmark '%s' contains illegal "
+                "character" % mark))
 
 def read(repo):
     '''Parse .hg/bookmarks file and return a dictionary
@@ -80,9 +80,7 b' def write(repo):'
     if repo._bookmarkcurrent not in refs:
         setcurrent(repo, None)
     for mark in refs.keys():
-        if not valid(mark):
-            raise util.Abort(_("bookmark '%s' contains illegal "
-                "character" % mark))
+        checkvalid(mark)
 
     wlock = repo.wlock()
     try:
@@ -113,9 +111,7 b' def setcurrent(repo, mark):'
 
     if mark not in repo._bookmarks:
         mark = ''
-    if not valid(mark):
-        raise util.Abort(_("bookmark '%s' contains illegal "
-            "character" % mark))
+    checkvalid(mark)
 
     wlock = repo.wlock()
     try: