templatefilters: add dirname() filter

This is different from stripdir() in that the last component is always
removed.

mercurial/templatefilters.py

@@ -100,6 +100,13 b' def count(i):'
     """List or text. Returns the length as an integer."""
     return len(i)
 
+@templatefilter('dirname')
+def dirname(path):
+    """Any text. Treats the text as a path, and strips the last
+    component of the path after splitting by the path separator.
+    """
+    return os.path.dirname(path)
+
 @templatefilter('domain')
 def domain(author):
     """Any text. Finds the first string that looks like an email

tests/test-command-template.t

@@ -2232,6 +2232,10 b' Filename filters:'
 
   $ hg debugtemplate '{"foo/bar"|basename}|{"foo/"|basename}|{"foo"|basename}|\n'
   bar||foo|
+  $ hg debugtemplate '{"foo/bar"|dirname}|{"foo/"|dirname}|{"foo"|dirname}|\n'
+  foo|foo||
+  $ hg debugtemplate '{"foo/bar"|stripdir}|{"foo/"|stripdir}|{"foo"|stripdir}|\n'
+  foo|foo|foo|
 
 Add a dummy commit to make up for the instability of the above: