Fix makefile dependence for system tests.
portfolio: fix export of emptyset
Fix two variants of Node::substitute().

Node::substitute() is overloaded.  One version was properly substituting
operators (e.g. the "f" in f(x) could be substituted).  The others were
ignoring anything in function position.  Fixed.  Thanks to Wei Wang for
pointing this out.
Merge branch '1.3.x'
reorganize substr, fix some potential bugs, adds cache for preprocessing
Merge branch 'master' of github.com:tiliang/CVC4