Fix the calculation of the total time on worker.

This introduces another task variable to keep track of when a task has
been committed to a worker.  This time is checked when a worker is
removed to avoid adding too much time to the total time on worker (due
to the task starting time being incorrect).
Clean iRODS paths to not have trailing slashes.

iRODS considers paths ending in a forward slash to be invalid and throws an
error.

Fixes #464.
Merge branch 'matz-e-master'
Merge branch 'master' of https://github.com/cooperative-computing-lab/cctools into deltadb
Add comment to fix in a8f3ade.
Stop compilation on building bindings error.
Correct WQ binding build error due to externals.

ND's iRODS is compiled without -fPIC so the linker terminates with an error
when trying to build the WQ binding shared libraries. This fix is a stopgap to
get the build working: we separate out the archives and shared libraries we
link against and only link against shared libraries for the WQ bindings.  Since
none of the WQ bindings depend on any external archives, this solves the
problem.

Ideally, we would separate out each individual external and dependency so we
could link only against what we want. However, that would be a much larger and
intrusive change to the build system.

Fixes #466.
Merge branch 'master' of https://github.com/cooperative-computing-lab/cctools into deltadb
deltadb_* instead of ddb_*
deltadb_pivot man page complete