Use correct -soname for qtgl shared library, so that libqtgl actually works.
Previously libqtgl.so.4 was libked with soname of libqt2.so.4, so that
when you link application with -lqtgl you are fine, but when you are trying
to run resulting application it dies because libqt2 (which has no GL code)
is dynamically linked instead.
Not objected by: will