Ensure byte code enhancer updates incremental compiler analysis

In SBT 0.13.1, a feature was added to the incremental compiler that meant that products (class files) were invalidated if their modification date changed, where previously the only check that was done was whether they existed.

Play's byte code enhancement enhances Scala template classes, and this enhancement was updating the modification date, naturally causing the incremental compiler to invalidate the classes on its next run, and recompiling them unnecessarily.  

This change updates the analysis object after Play has modified any template files, and then writes the updated analysis out to disk.