Fix a bug in the state cache mechanism. Refactor this a bit.

Fix a bug in the state cache mechanism.  Refactor this a bit.

cc-engine.el (c-parse-state-get-strategy): Remove the `cache-pos' element
from the return value.
(c-append-lower-brace-pair-to-state-cache): "Narrow" to end of buffer to
enable proper searching from beyond HERE.
Amend the test for detecting the sought brace pair.  Amend the value
written to the "brace desert cache" when the brace isn't found.
(c-remove-stale-state-cache): Rename `good-pos' to `start-point', and
several other variables analogously.
(c-remove-stale-state-cache-backwards): Change `cache-pos' from a
parameter to a locally calculated variable.
(c-parse-state-1): Change the calling conventions to the two defuns
involving `cache-pos'.