Sensitivity calculation bug

Update: here is a patch for ExprLib that exposes the bug, which shows up in trying to access the sensitivity of r2_u (2nd component of u RHS) to w, to which it is not connected. From test run ./sens-block-install. The executable is called sensitivityBlockInstallation.cpp.

ExprLib patch: exprlib-bug-exposer.patch

The attached PoKiTT patch has sensitivities implemented for pressure, speciesN, mixture molecular weight, and thermal conductivity (trivial sensitivities) and an executable that calculates these quantities from density, mass fractions, and temperature. When calculating the sensitivity of mixture molecular weight (MMW) to density, an error is thrown upon asking for the sensitivity of a mass fraction to density. This shouldn't happen because MMW is not connected to density.

Also attached is the mechanism file. To run the executable, go to build/test and use ./sensitivities --xml-input-file=h2-burke.xml.

PoKiTT patch: sensitivities-issue.patch

Mechanism input: h2-burke.xml