Added optional LOGGER_DEBUG(...) for verbose logs

By default LOGGER_DEBUG does nothing. To enable, build
with OPTFLAGS=-DDEBUG. This both turns off optimization
and turns on verbose debug output.
http_server_sendfile2()
http_server_get_app_context()
added hashtablefile_readonly_foreach()
mysql_helper_real_connect(), for setting options
missing include, missing free
http_client_free(): remove pool arg
lhashtable_foreach()
http_server: begin_cookie, end_cookie
improve daemonize, support multicore via fork
shutdown server when child process dies
object_pool bug fix

If somebody pulls 10 objects off pool, the pool grows ten objects,
then the 10 objects are put back in pool, vmbuf_unsafe_wseek
could cause segfault
ds_var_field_writer + minor fixes
added a macro for custom lib locations for ribify
Added UNIX datetime support for mysql_helper
fixed var index name in ds_loader
ignore SIGINT in child processes (mainly for gdb)
macro to declare idx struct
ds_loader: verify list of files
added TUTORIAL06: Ribifying MongoDB client