changes to thermostatic3wayValve:
1) added conditional state and initial condition for k
2) added parameters for limit values of k
add Thermostatic3WayValvePI.mo
solved issue where thermostatic3WayValve had a division by zero when the two incoming enthalpies are equal
Merge branch 'issue111_3wayValve' of github.com:open-ideas/IDEAS into issue111_3wayValve

it merges an updated upstream into a topic branch.
remove non-physical equation for k-factor of Thermostatic3WayValve.mo and replace it by a non-event boundary for the enthalpy.
removed thermostatic3WayValvePi
changes to thermostatic3wayvalve:
outlet enthalpy setpoint is calculated using more correct arguments
changed default valve leakage values
changed description of a variable
Merge pull request #112 from open-ideas/issue111_3wayValve

Changes to thermostatic3wayValve. A discontinuous change in "k" (i.e. a "Unbounded help variable for determining fraction of each flow") is still reported, but accepted.