bug#1212: 23.0.60; split-string-and-unquote problems

[Stefan Monnier <monnier@iro.umontreal.ca>]

>     *** `split-string-and-unquote' does (what?)
>     *** `combine-and-quote-strings' does (what?)

AFAIK, these two functions are meant to:

- provide a way to specify any list of strings within a single string
  (i.e. it needs to provide some separators and some way to quote the
  separators), using a format that's simple to type for the end user.
- be inverse of each other; more precisely
  (equal STR (split-string-and-unquote (combine-and-quote-strings STR)))
  this is also stipulated in the docstring of split-string-and-unquote.

As the docstring of split-string-and-unquote explains, the quoting used
is the same as the one used for ELisp strings.

I could have used sh-style quoting or csh-style, or any other style, but
csh-style is nasty, sh-style is too powerful (what should we do with
backquotes and $(...)), and ELisp is what Emacs uses already and it's
reasonably simple and we know it handles all cases reasonably well, so
it seemed like an OK choice.


        Stefan