Added xalloc.o to Makefile

added missing xalloc.o to Makefile as function "xmalloc" is used in logger and failed to complete linking of logger.o.
Merge pull request #158 from koroban/master

Added xalloc.o to forge socket Makefile
fix remaining time
Make -Werror optional via -DWITH_WERROR=ON

It was causing too many issues with yacc / lex
Automatically determine optimal number of senders

Use num_cores - 1 sender threads if --quiet is passed. Use num_cores - 2
if the monitor is running as it uses another thread.

Fixes #139
Output generator as int64 to prevent overflow

Fixes #140