SF: SB: Mutable pointer arguments

[iondev33]

In C++ code that uses ION, eids may be stored in c++ std::string objects. std::string is converted to a char pointer via the .c_str() method, which returns a const pointer. So, to safely pass these EID's into ION API functions that expect non-const arguments (e.g., bp_send's destEID parameter), it is necessary to make a mutable copy first. We should scrub the ION public API function prototypes of unnecessarily mutable pointer arguments.