`c-update-modeline' in cc-cmds.el has a long-standing bug (and FIXME
comment) whereby a `mode-name' which is not a string will trigger
errors, on account of the function using string manipulations to add
the minor mode flags to the original `mode-name'.

This is what bug #2034 was originally about. i.e.:

> c-update-modeline: Wrong type argument: stringp,
> (sgml-xml-mode "XML" "SGML")

This new patch instead uses mode-line constructs to concatenate the
flags, thus eliminating the string manipulation code and this bug.

In the process I've added a user option to allow the user to choose
whether or not these flags should be displayed at all, as this was not
previously configurable.

e.g.: `c-update-modeline' will now convert the mode-name "C++" into
'("C++" (c-modeline-display-flags c-modeline-flags)); and it only
updates the buffer-local value of `c-modeline-flags' which is then
conditionally displayed based on option `c-modeline-display-flags'.

This bug fix also resolves an incompatibility with the `delight'
package in GNU ELPA, which wraps any targeted `mode-name' values
in additional mode line constructs, and consequently triggered the
`c-update-modeline' bug with its assumption of a string, when used
with any of the major modes in question.

In my testing thus far this new approach seems to work nicely.


-Phil