MultiPDepArrhenius requires identical pressures in all PDepArrhenius objects.

This is so we can evaluate the k(T,P) values by evaluating the sum of the
k(T,P_1) and k(T,P_2) values across the different PDepArrhenius
expressions, then interpolating logarithmically in pressure. The idea is
that you need this sum-of-PLOG format to accurately capture the very
non-Arrhenius behavior of some pressure-dependent kinetics.
Fixed thermo groups commenting.
Change cyclic molecule check function to isCyclic() in thermo estimation.

This may speed up the cyclic check- don't start more expensive function
getSmallestSetOfSmallestRings() until we are sure molecule is cyclic.
Skips the function altogether if the molecule is polycyclic.
Merge branch 'master' of git://github.com/jwallen/RMG-Py

Conflicts:
	rmgpy/kinetics/arrhenius.pyx
Remove deprecated `checkDuplicateKinetics` function in chemkin reader.

Now using markDuplicateReactions instead.
Use species label when saving rotor scan plots in CanTherm jobs.

This enables the user to have multiple species in the same directory, but
still keep the plots of the hindered rotor scans.