templatefilters: fix crash by string formatting of '{x|splitlines}'

Before, it crashed because mapping['templ'] was missing. As it didn't support
the legacy list template from the beginning, we can simply use hybridlist().

mercurial/templatefilters.py

@@ -339,7 +339,7 b' def shortdate(text):'
 @templatefilter('splitlines')
 def splitlines(text):
     """Any text. Split text into a list of lines."""
-    return templatekw.showlist('line', text.splitlines(), {}, plural='lines')
+    return templatekw.hybridlist(text.splitlines(), name='line')
 
 @templatefilter('stringescape')
 def stringescape(text):

tests/test-command-template.t

@@ -3894,6 +3894,11 b' Test splitlines'
   o  foo line 1
      foo line 2
 
+  $ hg log -R a -r0 -T '{desc|splitlines}\n'
+  line 1 line 2
+  $ hg log -R a -r0 -T '{join(desc|splitlines, "|")}\n'
+  line 1|line 2
+
 Test startswith
   $ hg log -Gv -R a --template "{startswith(desc)}"
   hg: parse error: startswith expects two arguments