templatefilters: fix doc of basename() stable

templatefilters: fix doc of basename()

os.path.basename() does NOT strip trailing slashes.

> Note that the result of this function is different from the Unix basename
> program; where basename for '/foo/bar/' returns 'bar', the basename()
> function returns an empty string ('').
https://docs.python.org/2.7/library/os.path.html#os.path.basename

--- a/mercurial/templatefilters.py	Sun Jan 07 15:56:58 2018 +0900
+++ b/mercurial/templatefilters.py	Sun Jan 07 12:07:29 2018 +0900
@@ -90,9 +90,8 @@
 @templatefilter('basename')
 def basename(path):
     """Any text. Treats the text as a path, and returns the last
-    component of the path after splitting by the path separator
-    (ignoring trailing separators). For example, "foo/bar/baz" becomes
-    "baz" and "foo/bar//" becomes "bar".
+    component of the path after splitting by the path separator.
+    For example, "foo/bar/baz" becomes "baz" and "foo/bar//" becomes "".
     """
     return os.path.basename(path)
 

--- a/tests/test-command-template.t	Sun Jan 07 15:56:58 2018 +0900
+++ b/tests/test-command-template.t	Sun Jan 07 12:07:29 2018 +0900
@@ -2218,6 +2218,11 @@
   $ cd ..
   $ rm -rf unstable-hash
 
+Filename filters:
+
+  $ hg debugtemplate '{"foo/bar"|basename}|{"foo/"|basename}|{"foo"|basename}|\n'
+  bar||foo|
+
 Add a dummy commit to make up for the instability of the above:
 
   $ echo a > a