D: Add D nature to Eclipse projects
D: Improve how cmake's tests check for D

* Add an option to force D tests to run
* Mirror CheckFortran.cmake instead of using enable_language()
D: Fix rpath handling on Linux, OS X
D: Fix miscellaneous shared library flags for Linux
D: Fix typo in ddeps
D: Fix argument handling in ddeps setup

Correctly probe conditional compilation information in compilers
when the compiler has an argument (such as -m32).
D: Remove cl stuff from D compiler detection