TODO

* configure and --with-xxx:
  - the README is misleading on the use of --prefix; really need
    a --site-includes/--site-libraries flag
  - if a --with flag is given, the computed -L/dir options should appear
    up front, certainly before -L/usr/local/include
  - if --prefix is given, $prefix/lib and $prefix/include should be
    searched, but --with-xxx flags must take precedence
  - should we search /usr/local by default?

  - the --with-build-path flag is enabled, 
    still need to update the build docs

* use ICBM150 data as default model?

* configure probe for Getopt::Tabular

* it would be handy to be able to pass `-verbose 3' on to minctracc,
  but the handing of -verbose and -debug is currently done by some perl library
  code; maybe it could be triggered on -debug?  But what level to set?

* it would be nice if xcorr_vol could optionally take a transformation
  and apply it to one of the volumes