Fix incremental bug in symmetry breaker.

Thanks to Christoph Sticksel for reporting this.
Merge branch '1.2.x'
Fix an error that valgrind found.
Fix bug 512: an assertion failure only appearing with clang on Mac OS, due to improper ITE removal in quantifier instantiations.
Merge branch '1.2.x'
minor code clean up
spelling
clear up resource limit documentation