Fix the default XDG_DATA_DIRS paths
Silence an MSVC warning about -1u
Fix a NULL deref when cloning a 0-sized vector
Add a VECTOR_INSERT method to insert a range of elements at once
Insert all new effect slots into the active effect slots at once
Avoid referencing the start iterator twice for vector insertion
Pass in the vector insertion point as a pointer
Add a GCC-specific VECTOR_INSERT

This version is capable of doing a compile-time type checks, to ensure the
objects being inserted are compatible with the vector data type. It should
otherwise be functionally identical.
Use VECTOR_INSERT to copy and append strings
Use a helper to detect a path slash on Windows
Ensure VECTOR_ITER_BEGIN gives a pointer-to-type instead of an array-of-type
Avoid memory leak if preset ID lookup fails