Add --enable-strict-lgpl configure option

As discussed in Issue #224, this branch branch implements the --enable-strict-lgpl configure option.  I tried to see if I could name the option --strict-lgpl, but it seems that configure wants all options to be either `--enable-xyz` or `--with-xyz`...  

The patch is pretty straightforward and it seems to work for me, the packages which get turned off are below, let me know if I forgot any.

```
Optional Packages:
  laspack.......................... : no
  sfcurves......................... : no
  triangle......................... : no
```