Check for err.h and work around for AIX
added list_for_Zhinan_for_SPECFEM3D_PMLs.txt (items that need to be done for PMLs; we will remove that file when we are done)
updated list_for_Zhinan_for_SPECFEM3D_PMLs.txt
adds flexwin/ as a submodule to directory ADJOINT_TOMOGRAPHY_TOOLS/