Multiple fixes for work queue:
* "cancel tasks" works correctly and no longer segfaults
* foreman nodes use the correct value for their max_tasks (current workers vs total workers ever connected)
* worker no longer disconnects after a very long running task
* work queue master logs every message it sends in the debug log when D_WQ is enabled
Fixed va_copy mixup
added vdebug() to handle the arguments as a va_list instead of a normal list of arguments.
fixes a segfault in send_worker_msg when trying to print out the worker message
added long option to specify log filesize
added volatility option to work_queue_worker, to simulate failure
with "reliability".
Check for available disk space on each pass through the main loop,
so as to handle tasks that consume space quickly on output.
Display space error in units of megabytes.

Conflicts:
	dttools/src/work_queue_worker.c
Fixed parsing to be consistent with help message: disk space limit is expressed as plain number without units.
Previous code accepted units but didn't handle them correctly.
Add debug msg when resetting execv syscall number.
Merge branch 'master' of github.com:cooperative-computing-lab/cctools

Conflicts:
	dttools/src/work_queue_worker.c
Fixed bug: buffer_printf appends to the buffer, so buffer_tostring
is not needed (and caused a crash).