minor custom.el doc fix

[Per Abrahamsen]

Having punctuation marks inside quotes may be correct according to
some style guides, but are probably not a good idea for Emacs doc
strings, where symbols inside quotes are clickable.

2001-12-04  Per Abrahamsen  <abraham@dina.kvl.dk>

        * custom.el (defcustom): Doc fix (dot outside quotes).

*** custom.el.~1.46.~   Mon Nov 26 16:14:02 2001
--- custom.el   Tue Dec  4 18:40:20 2001
***************
*** 177,183 ****
        VALUE should be a function used to initialize the
        variable.  It takes two arguments, the symbol and value
        given in the `defcustom' call.  The default is
!       `custom-initialize-reset.'
  :set  VALUE should be a function to set the value of the symbol.
        It takes two arguments, the symbol to set and the value to
        give it.  The default choice of function is `custom-set-default'.
--- 177,183 ----
        VALUE should be a function used to initialize the
        variable.  It takes two arguments, the symbol and value
        given in the `defcustom' call.  The default is
!       `custom-initialize-reset'.
  :set  VALUE should be a function to set the value of the symbol.
        It takes two arguments, the symbol to set and the value to
        give it.  The default choice of function is `custom-set-default'.