field_simps: better support for negation and division, and power
#main components for everyday use, without big impact on overall build timecvc3-2.4.1e-1.8exec_process-1.0.3Haskabelle-2013jdk-7u40jedit_build-20140405jfreechart-1.0.14-1kodkodi-1.5.2polyml-5.5.1-1scala-2.10.4spass-3.8dsz3-3.2-1z3-4.3.0xz-java-1.2-1ProofGeneral-4.2-1