Allow a CC Mode derived mode to have strings delimited by single quotes.

Allow a CC Mode derived mode to have strings delimited by single quotes.

Also fix the bug where the delimiters of '\033', etc. got the error face.

* lisp/progmodes/cc-langs.el (c-single-quotes-quote-strings): Enhance the docr
string.
(c-string-delims): Change doc string to doc comment.

* listp/progmodes/cc-mode.el (c-before-change-check-unbalanced-strings): In
searches and comparisons, take account of the string delimiters possibly
being '.  Fix argument in call of c-before-change-check-unbalanced-strings.
(c-parse-quotes-before-change, c-parse-quotes-after-change): Bind
case-fold-search to nil.  Analyze escape constructs inside character constants
more accurately, in particular accepting as valid more than one character
after /[0-7], /x, /u, and /U.  Amend calculations to account for this extra
length.