Looking for libjpeg-turbo in the default install location before /usr/include.

Since libjpeg-turbo can be used to more than tinia, the libraries sometimes exist on the system as part of another package. If we have installed libjpeg-turbo ourselves, it is most likely found in the /opt/ folder, and we should therefore look for the libraries there before we look in /usr/include.

This was found to be a problem for at least two persons, and the restructuring of hint directories commited here fixed their problems.
Merge pull request #129 from sintefmath/havahol_cmakeJPEG_smallFix

Very small change in CMakeLists.txt