Previously, dependencies were not correctly searched for as
required packages. This patch fixes this.

Previously we relied on CMake's export(PACKAGE ...) function when
finding dune packages without dune-control. This is error prone
when using several instances of a dune-module (either with differing
versions or built using different options). In this case there is no
control which of the instances is used.

Now we try to guess the correct build directory, if it was not
provided with ${module}_DIR, ${module}_Root or in the
CMAKE_PREFIX_PATH. Note that when using dunecontrol ${module}_DIR will
always be set. We take the path of the current toplevel build
directory and simply substitute any occurence of the name of current
module with name of the module that we try to find. This works for
both  building in a subdirectory of the source tree
(e.g. ${module-source}/build-cmake) or in a sibling directory

Renamed CMAKE_(SOURCE|BINARY)_DIR to PROJECT_(SOURCE|BINARY)_DIR to let people build dune modules as subproject of another project.

[[Imported from SVN: r1791]]

Some of the macros used are only available for CMake 2.8.6 and higher. Bumped required CMake version

[[Imported from SVN: r1727]]

  after configure)
- Make CMake module installation path configurable
- Detect CMAKE_MODULE_PATH automatically
  + First call find_package(dune-common) to query its CMAKE_MODULE_PATH
  + Then setup the module path
  + After each find_package of dune module update the CMAK_MODULE_PATH
  + each module exports ist own <package-name>_MODULE_PATH in the
  + package configuration files

[[Imported from SVN: r1714]]

- Removed dependency on cmake version 2.8.9

[[Imported from SVN: r1707]]

[[Imported from SVN: r1676]]

[[Imported from SVN: r1596]]

[[Imported from SVN: r1556]]