ld can't find a library - g++

Question

Here is a Makefile:
all: main
bar.cxx:
echo "void bar(){}" > bar.cxx
foo.cxx:
echo "void bar();" > foo.cxx
echo "void foo(){ bar(); }" >> foo.cxx
main.cxx:
echo "void foo();" > main.cxx
echo "int main(){ foo(); }" >> main.cxx
%.o: %.cxx
g++ -c -fPIC $<
libbar.so: bar.o
g++ -shared -o libbar.so bar.o
libfoo.so: foo.o libbar.so
g++ -shared -o libfoo.so foo.o -L. -Wl,-rpath,\$$ORIGIN/. -lbar
main: main.o libfoo.so
g++ -o $# main.o -L. $(PWD)/libfoo.so
clean:
rm -rf *.so *.o *.cxx main
which fails like this on Ubuntu 14.04:
$ make
echo "void foo();" > main.cxx
echo "int main(){ foo(); }" >> main.cxx
g++ -c -fPIC main.cxx
echo "void bar();" > foo.cxx
echo "void foo(){ bar(); }" >> foo.cxx
g++ -c -fPIC foo.cxx
echo "void bar(){}" > bar.cxx
g++ -c -fPIC bar.cxx
g++ -shared -o libbar.so bar.o
g++ -shared -o libfoo.so foo.o -L. -Wl,-rpath,\$ORIGIN/. -lbar
g++ -o main main.o -L. /media/david/data/tmp/origin/libfoo.so
/usr/bin/ld: warning: libbar.so, needed by /media/david/data/tmp/origin/libfoo.so, not found (try using -rpath or -rpath-link)
/media/david/data/tmp/origin/libfoo.so: undefined reference to `bar()'
collect2: error: ld returned 1 exit status
make: *** [main] Error 1
RPATH is set relative:
$ objdump -p libfoo.so | grep RPATH
RPATH $ORIGIN/.
ldd print the correct path to libbar.so:
ldd libfoo.so
linux-vdso.so.1 => (0x00007ffe3f1c8000)
libbar.so => /media/david/data/tmp/origin/././libbar.so (0x00007f83c29ff000)
I have some questions, maybe in wrong order or redundant:
0) Why ld can't find libbar.so?
1) Why do I need to add -Wl,rpath,$(PWD) like below, while libfoo.so already contains the rpath?
main: main.o libfoo.so
g++ -o $# main.o -L. -Wl,-rpath,$(PWD) $(PWD)/libfoo.so
2) LD_LIBRARY_PATH=. make solve the problem, but why? I was thinking the LD_LIBRARY_PATH was used only at execution.
3) Why does -L. has no effect?