mangle C++ ::std and ::std::allocator correctly
Merge pull request #3873 from WalterBright/std-mangling

mangle C++ ::std and ::std::allocator correctly
[Refactoring] Clean up syntaxCopy functions

Dsymbol, Statement, Expression, Type, and Initializer.
Merge pull request #3886 from 9rnsr/refactor_syntaxCopy

[Refactoring] Clean up syntaxCopy functions