Currently this bootstrapper only finds the macros that are located
in the cmake/ tree in this project. Projects that don't carry their
own build system can specify search locations here.
Introduce a main build file which uses modules in the cmake/ directory
for most of its bulk work, which agains retrieve information from files
in the root of the source tree (dune.module, CMakeLists_files.cmake) to
get information about the project.
Thus, the cmake/ directory is shared between all the projects down to
the last bit; only project-specific customizations go into the main file
in form of _hook macros (which are called in specific places).
This let you specify a bunch of directory names on the command line
to *all* packages, without getting annoying warnings that they are
defined but not used.
Fall back to Eigen's BiCGSTAB solver if UMFPACK is not available. The
BiCGSTAB is built into Eigen and consequently always available when
Eigen is found.
Not all systems provide UMFPACK so even if Eigen provides the required
bindings, we should not assume that the underlying library and/or
headers are available. Currently, only examples/sim_simple.cpp uses
UMFPACK unconditionally, so the simplest solution is to exclude that
example unless UMFPACK is available.
