Properly version libjsoncpp.so.
Fix the problem described in bug 200969: currently, libjsoncpp.so is not
properly versioned by SCons; in other words, there's no SONAME in the
library's ELF header, which confuses the linker when creating binaries that
link against it.
Solve it by using InstallVersionedLib(), available since SCons 2.3.0: this
call is able to properly version the shared library the way we need it.
Since there is no support for actually installing the files outside the
build directory, we have to recreate the required symlinks ourselves in the
Makefile. Another related change is that we now create the libraries with
the proper names instead of doing that in the Makefile.
I'm (ab)using the maintainer's approval given to bug 200939, as swills's
latest patch includes this change as well.
Approved by: firstname.lastname@example.org (maintainer)