Modified dependency checking so as to issue a simple warning rather than a run-time error when a package is missing
Modified dependency checking so as to issue a simple warning rather than a run-time error when a package is missing

alexis-roche/niseg,bthirion/nipy,arokem/nipy,alexis-roche/register,alexis-roche/nireg,arokem/nipy,arokem/nipy,bthirion/nipy,alexis-roche/niseg,arokem/nipy,nipy/nireg,alexis-roche/nipy,bthirion/nipy,alexis-roche/nipy,bthirion/nipy,alexis-roche/register,nipy/nireg,nipy/nipy-labs,nipy/nipy-labs,alexis-roche/nipy,alexis-roche/register,alexis-roche/nipy,alexis-roche/nireg