Mod string generation to avoid faulty int concat

JCodeFile::scanBasicStats() was used the string concatenation operator
('+') to string together various clauses in its output.  However, this
approach failed to work correctly when int variables were used.  The +
operator does not have an overload that implicitly converts the integer
to a string as originally expected.

To rectify this, a std::stringstream was used instead of a string.
std::stringstream is unique in that its '<<' operator does the implicit
conversion from int vars to string literals that the '+' operator lacked
with strings.