Disable testing if BUILD_TESTING is switched off

This is an "official" switch for disable testing; our own code which
adds tests should adhere to it. (It is added by CTest)
Add a switch for examples similar to the one for tests

Running tests during development at least has a purpose, but compiling
all the samples *every* time is just an annoyance.
Let the AutoTools script disable tests and samples also
Merge pull request #292 from rolk/292_fastbuild

Add possibility to skip building tests and examples
Make project buildable also without Git

If Git is not found, revert to just dumping the label into the code.
(We currently have no way of getting the SHA into the tarball).
Merge pull request #293 from rolk/293_wogit

Make project buildable also without Git
Fix non-unit tests so that they compile again

Account for header, namespace and API changes.
Graduate these tests to unit tests

Although they don't use Boost::UnitTest, they can at least pass, so we
can use them to detect simple compilation and runtime errors, although
we miss the semantic check.

(If you have time, please make them proper unit tests)
Convert Cartesian grid test to use Boost::UnitTest
Cartesian grid test is now a proper unit test
Convert cubic interpolator to use Boost::UnitTest
Convert testing of metric units to use Boost::UnitTest
Graduate testing of metric unit to a proper unit test

Notice the confusing naming.
Add warning that this directory is not actively maintained.
Define API version macros for other code to query

Note the distinction between the version (1.0) and the release label
(2013.03). The latter is not really usable to check for API
compatibility. (See <http://www.semver.org>).
Insert remainder to keep version number is sync.
Rename test itself to not conflict with local variable
Indent consistently with whitespace instead of tab
Merge pull request #294 from rolk/294_unittests

Fix non-unit tests so they compile again
Only display an error message if C++11 support is noted as REQUIRED