Merge pull request #1 from mvassilev/master

Protect against users calling Derive with a wrong ValueDecl.
Merge pull request #2 from mvassilev/master

Improve test diagnostics and improve derivable argument evaluation.
Update README.md
Merge pull request #3 from mvassilev/master

Identifier name changes. Correct argIndex usage of callee functions.
Update to the newest llvm trunk.
Add a last known good llvm svn revision.
Merge branch 'master' of https://github.com/vgvassilev/clad

Conflicts:
	lib/Differentiator/DerivativeBuilder.cpp
Fix cloning of statements.
The references of IfStmts are now updated and Sema is used for visiting return
stmts.
Test results are evaluated and out files are generated.
No need for updateReferencesOf to return Expr*.
Making it return void.