Fix miscellaneous glitches in cc-mode.el. Fixes debbugs#20245.

Fix miscellaneous glitches in cc-mode.el.  Fixes debbugs#20245.

* progmodes/cc-mode.el (c-common-init): bind
\(before\|after\)-change-functions to nil around invocations of
c-get-state-before-change-functions and
c-before-font-lock-functions to prevent recursive invocations.
(c-neutralize-syntax-in-and-mark-CPP): On c-beginning-of-macro,
check that point has actually moved back.
(c-fl-decl-start): Check whether c-beginning-of-decl-1 has
actually found a boundary (as contrasted with hitting a search
limit).