It's now crossplatform wrapper for std::system opening of a file/path/url.
It returns an int just like std::system, 0 means it worked.
It's static so you don't need to gViewerWindow->getWindow() anymore,
honestly it should've been static in the first place.
Clean up other code to use this function because duplicate code sucks.
# Conflicts:
# indra/llwindow/llwindowmacosx.h
# indra/llwindow/llwindowsdl2.cpp
This introduces some API changes, like the new LLDirIterator,
that causes changes elsewhere.
It also include Log Linden's cache changes that aren't in
viewer-development yet that increase the maximum cache size
to ~10 GB.
