Fix an indentation bug:

Fix an indentation bug:

progmodes/cc-mode.el (c-common-init): Initialise c-new-BEG/END.
(c-neutralize-syntax-in-and-mark-CPP): c-new-BEG/END: Take account
of existing values.

progmodes/cc-engine.el (c-clear-<-pair-props-if-match-after)
(c-clear->-pair-props-if-match-before): now return t when they've cleared
properties, nil otherwise.
(c-before-change-check-<>-operators): Set c-new-beg/end correctly by
taking account of the existing value.

progmodes/cc-defs.el (c-clear-char-property-with-value-function): Fix
this to clear the property rather than overwriting it with nil.