Rewrite `StructLiteralExp::toElem` to store individual fields instead of generating a constant to fill the entire struct with a single `store`. This is much more efficient at compile time (fixing #320) and vastly reduces the size of the emitted code. Since LLVM no longer needs to keep the data for all fields in "registers" until the store happens, it should also be more efficient at run time in cases where the fields aren't assigned with constants. There's also some code clean-up by removing duplicated logic.

We have two different test sets. For the test drivers
you need do compile the .d files in this folder with
a Phobos D compiler.

To run the 'mini' test suite run
./runminitests

To run the DStress based tests execute
./runtest tmp-sensible-name
and then use 
./findregressions old-results new-results 
to display a list of regressions. You can
download old result files from
http://www.incasoftware.de/~kamm/ldc/reference