indicate forced builds in --dry-run output

forced builds are now marked with an 'F':

```
$ eb HDF5-1.8.11-goolf-1.4.10.eb gzip-1.5-goolf-1.4.10.eb --try-toolchain=goolf,1.5.14-no-OFED -Dr --force
Couldn't import dot_parser, loading of dot files will not be possible.
== temporary log file in case of crash /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV/easybuild-GaGTzg.log
Dry run: printing build status of easyconfigs and dependencies
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/g/GCC/GCC-4.8.2.eb (module: GCC/4.8.2)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/h/hwloc/hwloc-1.8.1-GCC-4.8.2.eb (module: hwloc/1.8.1-GCC-4.8.2)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/o/OpenMPI/OpenMPI-1.6.5-GCC-4.8.2-no-OFED.eb (module: OpenMPI/1.6.5-GCC-4.8.2-no-OFED)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/g/gompi/gompi-1.5.14-no-OFED.eb (module: gompi/1.5.14-no-OFED)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/o/OpenBLAS/OpenBLAS-0.2.8-gompi-1.5.14-no-OFED-LAPACK-3.5.0.eb (module: OpenBLAS/0.2.8-gompi-1.5.14-no-OFED-LAPACK-3.5.0)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/f/FFTW/FFTW-3.3.4-gompi-1.5.14-no-OFED.eb (module: FFTW/3.3.4-gompi-1.5.14-no-OFED)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/s/ScaLAPACK/ScaLAPACK-2.0.2-gompi-1.5.14-no-OFED-OpenBLAS-0.2.8-LAPACK-3.5.0.eb (module: ScaLAPACK/2.0.2-gompi-1.5.14-no-OFED-OpenBLAS-0.2.8-LAPACK-3.5.0)
 * [x] /Users/kehoste/work/easybuild-easyconfigs/easybuild/easyconfigs/g/goolf/goolf-1.5.14-no-OFED.eb (module: goolf/1.5.14-no-OFED)
 * [ ] /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV/tweaked_easyconfigs/zlib-1.2.8-goolf-1.5.14-no-OFED.eb (module: zlib/1.2.8-goolf-1.5.14-no-OFED)
 * [x] /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV/tweaked_easyconfigs/Szip-2.1-goolf-1.5.14-no-OFED.eb (module: Szip/2.1-goolf-1.5.14-no-OFED)
 * [F] /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV/tweaked_easyconfigs/gzip-1.5-goolf-1.5.14-no-OFED.eb (module: gzip/1.5-goolf-1.5.14-no-OFED)
 * [ ] /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV/tweaked_easyconfigs/HDF5-1.8.11-goolf-1.5.14-no-OFED.eb (module: HDF5/1.8.11-goolf-1.5.14-no-OFED)
== temporary log file /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV/easybuild-GaGTzg.log has been removed.
== temporary directory /var/folders/8s/_frgh9sj6m744mxt5w5lyztr0000gn/T/easybuild-sKZhxV has been removed.
```
```