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>
Documentation rearrangement.
Clickfs: Fix a potential SMP problem.

'XXX locking' is a good place to look for potential SMP problems.
Make sure that all access to click_ino is protected by LOCK_CONFIG_READ().
ino: fix weird placement new

This placement new was assuming that the String it constructs is the first
member of the struct.  Instead, find the String member explicitly.
ino: use snprintf instead of sprintf

The sprintf used in this code is potentially unsafe, especially on 64-bit
platforms.  While it is unlikely that we'll break a 10 byte buffer, switch
to a 20-byte buffer (2^64 ~ 1.8e19) and pass that length into snprintf.