Import needed packages before exec command during database loading.
Import needed packages before exec command during database loading.

This is so that we can load the database in compiled Cython mode, which
doesn't allow package imports that occur as a result of using the exec
command. In particular, this was noticed when reading ThirdBody and
derived classes, as colliders are represented as SMILES strings which
require OpenBabel to process.

faribas/RMG-Py,faribas/RMG-Py,enochd/RMG-Py,KEHANG/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,enochd/RMG-Py,KEHANG/RMG-Py,pierrelb/RMG-Py,chatelak/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py,comocheng/RMG-Py,nyee/RMG-Py,pierrelb/RMG-Py