indent based on subsequence of symbol

[Lucien Pullen]

Also sprach Luís Oliveira on 2013-10-11:
> slime/contrib/swank-indentation.lisp also has a customization
> mechanism as well, *application-hints-tables*, which might be useful
> if you want to do it on the Common Lisp side.

I've made a modification to swank-indentation.lisp to allow functions to
be called to get the indentation rule, but I've run into a bit of a
snag...  The indentation rule will be used when the form is the first
form that needs to be looked up from *application-hints-table*.

Indentation now works like this (when given the rule (AS LAMBDA)):

  (defun test ()
    (x!html ()
      (x!head ()
              ...)
    ...))

I assume this has something to do with the way symbols are looked up,
but I'm not sure where things get lost.  Any pointer in the right
direction will be appreciated.