Rename a variable for clarity.
Rename a member function and drop its argument, since the data passed there is duplicative of what we have elsewhere.
Changes in manual regarding compressibility and Juliane's fixes to certain terms
fix up manual after 1baf0382dc80
temporarily fix convection-box.prm until we figure out what happens with the linear solver.
Merge remote-tracking branch 'geodynamics/master' into direct_solve