/usr/lib/libqgis_core.so is in libqgis-dev 1.7.4+1.7.5~20120320-1.1+b1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libqgis_core.so.1.7.5
/usr/lib/libqgis_core.so.1.7.5