Ubuntu/Debian introduced "multiarch" library directories, which is
unsupported by CMake <= 2.8.10. Add manual search paths as a workaround.
Currently it is only needed for libsvn, but it is needed for any lib
which is converted to the new directory standard.
Distros like Debian/Ubuntu use architecture-specific directory structures
(like /usr/lib/x86_64-linux-gnu) which we cannot hardcode/guess, so we
really need to search the default paths.
Don't detect libsvn without APR.
When installed, enable libsvn support by default (same as for automake).
When enabled, provide libsvn to fgfs.
gitignore temporary CMake files