If the user did not want integral control and set i_gain_ to zero,
then dividing by i_gain_ would set i_error_ to NaN.  This is not
desired.  Instead, replace the use of division to create i_term
with direct integration of i_term_.

Replace private member i_error_ with i_term_.

In getCurrentPIDErrors() create & return i_error_ with the same old meaning and units.
NOTE: i_error_ is not needed internally anywhere else.
Merge branch 'test-bad-integral-bounds' into fix-PID-unbounded-i_error
Merge branch 'test-bad-integral-bounds' into fix-PID-unbounded-i_error
Resolving conflict from new Pid API
Merge typo
Merge branch 'fix-pid-backwards-compatibility' into fix-PID-unbounded-i_error
Adding Bob's fixes to the backwards-compatibility API
Merge branch 'fix-pid-backwards-compatibility' into fix-PID-unbounded-i_error
Merge branch 'master' into fix-PID-unbounded-i_error
Fixing merge error
Merge pull request #1 from jbohren-forks/fix-PID-unbounded-i_error

Adding tests to show problems with integral term in ros_control pid_toolbox
Merge pull request #14 from bobholmberg/fix-PID-unbounded-i_error

Using zero i_gain_ to turn off integral control did unsavory things.