1. Another set of arguments optimized:
* args-by-val converted to args-by-ref
* in some cases, reverse has been done, if that is better: if the
object's copy is modified in the func, it's better to avoid extra copy
from arg to local var
2. some const functions marked as such (this is just a beginning)
3. iterators were replaced with const_iterators where applicable
4. catches that catch std::exception& changed to catch (...) - that is
safer; if exception handling is restructured, this will have to be
reconsidered anyway
5. removed some basic structures' constructors; changed them to hold
const char*s to avoid unnecessary string constructions;
6. in some places, moved variable declarations to their definitions, to
avoid calling default constructors and then assigning
7. removed some unnecessary shared_pointers in favor of local objects;
8. in FORTRAN-style functions, added const specifiers to input doubles;
9. fixed a place where values were inserted into a map while iterating
through it
10. fixed is_valid_*_derivative: they could accept incorrect values and
throw when upper index is less than lower
