Use t for non-nil default values in boolean defcustom declarations

Use t for non-nil default values in boolean defcustom declarations

* lisp/emulation/viper-ex.el (ex-unix-type-shell):
* lisp/emulation/viper-init.el (viper-ms-style-os-p):
* lisp/eshell/em-glob.el (eshell-glob-case-insensitive):
* lisp/filecache.el (file-cache-ignore-case):
* lisp/lpr.el (lpr-add-switches):
* lisp/ls-lisp.el (ls-lisp-ignore-case):
* lisp/mail/binhex.el (binhex-use-external):
* lisp/progmodes/cperl-mode.el (cperl-electric-parens-mark):
Normalise default values to nil or t.