Pengaruh struktur kepemilikan saham institusional, jumlah dewan direksi, jumlah komite audit dan pengungkapan corporate social responsibility (CSR) terhadap nilai perusahaan PT Bumi Resources, Tbk periode 2007- 2011 = The Influence of institutional ownership, size of board of directors, size of audit committee and corporate social responsibility disclosure on firm value of PT Bumi Resources, Tbk period 2007-2011