Relax editor templating

I tried to set my editor to `termite -e "vim -f {}"`, termite being a
pretty cool and light terminal I use within my i3wm Arch linux box.

So when I open my editor I want it to launch a terminal with Vim inside
instead of GVim for various reasons.

The validation rejected this at first because it was looking for '{}'
inside ['foo', 'bar', 'baz {}'], essentially. So I need it to look
inside the sub-strings, not just the list.

Then after validation I need to perform the '{}' replacement inside the
sub-string too, not just replacing the whole string.

qutebrowser/config/configtypes.py

@@ -1094,7 +1094,7 @@ class ShellCommand(BaseType):
             shlex.split(value)
         except ValueError as e:
             raise configexc.ValidationError(value, str(e))
-        if self.placeholder and '{}' not in self.transform(value):
+        if self.placeholder and '{}' not in value:
             raise configexc.ValidationError(value, "needs to contain a "
                                             "{}-placeholder.")
 

qutebrowser/misc/editor.py

@@ -124,6 +124,6 @@ class ExternalEditor(QObject):
         self._proc.error.connect(self.on_proc_error)
         editor = config.get('general', 'editor')
         executable = editor[0]
-        args = [self._filename if arg == '{}' else arg for arg in editor[1:]]
+        args = [arg.replace('{}', self._filename) if '{}' in arg else arg for arg in editor[1:]]
         log.procs.debug("Calling \"{}\" with args {}".format(executable, args))
         self._proc.start(executable, args)