core.runtime: loadLibrary and unloadLibrary?

[Martin Nowak]

> About D shared libraries, this is what's missing:
> 
> The runtime need to collect the following from all loaded images (shared
> libraries and executables) and all that are loaded during program
> execution:
> 
> * Exception handling tables
> * Ranges scanned by the GC
> * TLS data
> 
> There are more issues than listed above that I can remember right now.
> 

Right this is the same state on POSIX and of 2.061 all shared libraries
produced by dmd try to call a weakly linked `_d_dso_registry` upon
loading/unloading to pass EH and ModuleInfo tables.
https://github.com/D-Programming-Language/dmd/pull/1043/files#L0R3112

The current state of:
https://github.com/dawgfoto/druntime/tree/SharedRuntime
https://github.com/dawgfoto/phobos/tree/SharedRuntime
is here:
http://forum.dlang.org/post/op.wcrffp2asqugbd@localhost

Some unsolved issues remain:
http://forum.dlang.org/post/mailman.2052.1325532031.24802.digitalmars-d@puremagic.com