Make util phexdigit array reusable

class template base_uint had its own private lookup table.
This is saving 256 bytes per instantiation.

The result is not spectacular as bitcoin-qt has only shrinked of
about 1Kb but it is still valid improvement.

Also, I have replaced a for loop with a memset() call.

Made CBigNum::SetHex() use the new HexDigit() function.

Signed-off-by: Olivier Langlois <olivier@olivierlanglois.net>
make -logtimestamps default on and rework help-message
Refactor: CTxMempool class to its own txmempool.{cpp,h}
Merge pull request #3154 from gavinandresen/mempool_refactor

Mempool refactor
process received messages one at a time without sleeping between messages
Merge pull request #3180 from pstratem/processgetdata

Reduce latency in network processing
Merge pull request #3076 from lano1106/uint256_util

 Make util phexdigit array reusable
Merge pull request #3188 from Diapolo/logtimestamp_def

make -logtimestamps default on and rework help-message
qt: add license header to source files

Closes #839
Make time facet non-constant
Merge pull request #3197 from laanwj/2013_11_qt_license

qt: add license header to source files
Merge pull request #3198 from nvmd/compile_on_mavericks

Make time facet non-constant