Patch by Dan Liew: "fixed mistake in autoconf substitution variable name."

git-svn-id: https://llvm.org/svn/llvm-project/klee/trunk@160792 91177308-0d34-0410-b5e6-96231b3b80d8
Patch by Dan Liew that adds support for building Doxygen out-of-source.

git-svn-id: https://llvm.org/svn/llvm-project/klee/trunk@160795 91177308-0d34-0410-b5e6-96231b3b80d8

Conflicts:

	configure

Due to conflict I decided to rebuilt configure from scrach by running the autoregen script.
Patch by Dan Liew that removes our internal copy of STP, and makes the --with-stp option mandatory:
"1. At configure time the --with-stp= option is now mandatory.
 2. The HAVE_EXT_STP macro has been removed.
 3. The ENABLE_EXT_STP autoconf replacement variable has been removed and consequently the Makefile variable of the same name has been removed."

git-svn-id: https://llvm.org/svn/llvm-project/klee/trunk@161055 91177308-0d34-0410-b5e6-96231b3b80d8

Conflicts:

	Makefile.common
	tools/klee/Makefile
	unittests/Expr/Makefile
	unittests/Ref/Makefile
	unittests/Solver/Makefile

Some mistakes in unittests/Expr/Makefile
unittests/Ref/Makefile doesn't exist in KLEE-CL
Fix compilation of unit tests (they still don't pass yet!).
This was due to ConstantExpr being replaced with IConstantExpr (see commit 04779d19c80e7b6bdb370485b63170d10506558b).
Later on this changed back to ConstantExpr (se commit 8bfde3a7866eb68aced9ac34a9ae02b80c56007f)