Linuxmodule fix: Avoid race condition in clickfs.

Derrick Pallas observed a race when the handler_strings array grows.
Solution: A list of HandlerString objects, rather than a growable
array of Strings (where another thread might reference the OLD array).
The HandlerString object also cleans up the code.

Authors: Derrick and Eddie
Signed-off-by: Eddie Kohler <ekohler@gmail.com>